American AA-1B TR-2?

[Warren Dunes]

I just made an appointment to go look at one. It has the 1580 pound gross weight and "bigger"34 gallon fuel system, O-235-C2C, and 7157 prop. It is supposed to be a 133 mph, 7 gph airplane with enough range with full tanks, and enough payload for my mission: one 250 statute mile flight about 14 times a month with one 180 pound pilot and 20 pounds of baggage. I also need to be able to carry a 140 pound passenger and another 20 pounds of baggage on an irregular basis.

Midwest USA, O & D airports at about 500 ft AMSL, highest terrain feature about 2000 ft AMSL. 7153 prop is also approved for type-- and was standard on trainer version. "Required" trips will be flown well under gross weight.

Does anyone have first hand or reliable second hand experience with the type?

Any quirks? Or things to look at closely?

Thanks.

 

[Rich Holt]

I love my Traveler. It has 2 more seats. I went to see a TR2 before I bought Peggy though. The only downside that I saw was that the TR2 was built as the trainer version of the Yankee. It is slightly slower than the other 1B. It has tighter controls that are really light which can be over-controlled easily. Also, the castering nose wheel takes some getting used to. With about an hour of training, all of those "issues" were resolved.

 

[Grum.Man]

These same questions come up pretty regularly on here so a search will answer a lot. I had an original AA1 with the "hot wing". It's an enjoyable airplane to fly. Controls are light and responsive, great visibility and decent room. They can be a little tight on leg room if you are long legged. While they are indeed faster than it's competition, I didn't get book cruise speeds and I don't think most do either. Most are 5-10 kt slower than claimed. It's about the cheapest airplane you could own. The annuals are quick and easy and there aren't a lot of gotchas. There is an AD for routine inspection of the elevator spring cartridge but it's not that expensive to fix. If it doesn't have an oil cooler I would add one. Check the flaps and ailerons for excessive play in the hinges. The fuel sight glasses are prone to leak but it's an easy fix. The only other issue I had was fuel leaks at the wing root. There is a rubber hose that connects the fuel tanks to the airframe that will eventually go bad. They are not easy to replace and require cutting an inspection hole under the wing near the root. If it has an inspection cover there, the hoses have already been done.

 

[Warren Dunes]

I love my Traveler. It has 2 more seats. I went to see a TR2 before I bought Peggy though. The only downside that I saw was that the TR2 was built as the trainer version of the Yankee. It is slightly slower than the other 1B. It has tighter controls that are really light which can be over-controlled easily. Also, the castering nose wheel takes some getting used to. With about an hour of training, all of those "issues" were resolved.

Looking at the Yankee website, the AA-1B was made in a "Trainer" version with a 7153 prop, and a "Traveler-2" version with the 7157 prop. The TR-2 offered as an option two 17 gallon tanks instead of two 12 gallon tanks (two gallons being unusable regardless). Four fuel fillers but only two tanks. Both props are on the type certificate, so they can be swapped out by any A&P. On paper, the climb prop offers seven percent shorter take-offs and faster rate of climb. The cruise prop offers four percent greater speed and range.

There are a few AA-5 Travelers for sale out there, one looks fantastic on the web, but it is more airplane than I need.

 

[Warren Dunes]

I had an original AA1 with the "hot wing".

Did the original wing have stall strips? (I have read three different versions of this.)

I didn't get book cruise speeds and I don't think most do either.

IIRC, before she became famous J.K.Rowling wrote aircraft performance data for all the GA manufacturers.

There is an AD for routine inspection of the elevator spring cartridge but it's not that expensive to fix. If it doesn't have an oil cooler I would add one. Check the flaps and ailerons for excessive play in the hinges. The fuel sight glasses are prone to leak but it's an easy fix. The only other issue I had was fuel leaks at the wing root. There is a rubber hose that connects the fuel tanks to the airframe that will eventually go bad. They are not easy to replace and require cutting an inspection hole under the wing near the root. If it has an inspection cover there, the hoses have already been done.

Thank you, this is precisely what sort of information I was looking for.

 

[Grum.Man]

Did the original wing have stall strips? (I have read three different versions of this.)


IIRC, before she became famous J.K.Rowling wrote aircraft performance data for all the GA manufacturers.


Thank you, this is precisely what sort of information I was looking for.

Yes it had the stall strips. There was nothing unusual or dangerous about how it stalled. The difference is a Grumman will stall where as most trainers will just mush down with the controls in your lap as long as you are coordinated. In my 150 I could hold the yoke all the way back, you would get a slight drop of the nose followed by a 500 fpm decent. In the Grumman you will get a slight buffet, then the nose will drop and require releasing the back pressure to recover.

 

[Warren Dunes]

There was nothing unusual or dangerous about how it stalled.

The 642-415 is just a semi- symmetrical (very nearly symmetrical) airfoil, but some people can't seem to figure out the Porterfield or Taylorcraft wing either.

 

[eman1200]

….Thank you, this is precisely what sort of information I was looking for.

Grum.man is the.man

 

[Grum.Man]

The 642-415 is just a semi- symmetrical (very nearly symmetrical) airfoil, but some people can't seem to figure out the Porterfield or Taylorcraft wing either.

The flap switch is also prone to failure. It sits right under the canopy bow so any water that leaks, leaks right onto the switch. It's an expensive little bugger so operate it several times to make sure it's good. You have to hold it down for the flaps to deploy. When you want the flaps up it will stay in the retract position so you don't have to hold it. There are inspection covers where the gear enters the airframe. There are large aluminum brackets that attach the gear to the spar. Check those for corrosion. The nose spring rod is supposed to be pulled, inspected, cleaned, and greased during the annual but nobody ever does. Lastly check the nose wheel fork for cracks and ensure the bearings are properly pre-loaded so you don't get nose wheel shimmy.

 

[Warren Dunes]

The flap switch is also prone to failure. It sits right under the canopy bow so any water that leaks, leaks right onto the switch...

Actually my biggest reservation concerning the type is rain.

It's an expensive little bugger so operate it several times to make sure it's good. You have to hold it down for the flaps to deploy. When you want the flaps up it will stay in the retract position so you don't have to hold it. There are inspection covers where the gear enters the airframe. There are large aluminum brackets that attach the gear to the spar. Check those for corrosion. The nose spring rod is supposed to be pulled, inspected, cleaned, and greased during the annual but nobody ever does. Lastly check the nose wheel fork for cracks and ensure the bearings are properly pre-loaded so you don't get nose wheel shimmy.

Thank you. A couple of posts mention "center caps," which being plural I take to be different than the rudder cap.

Looking at Aviation Safety Network I kept seeing phases like "fuel selector was set on empty tank," and "during high speed, low altitude pass," and "aircraft was overweight with CG aft of limits..."

 

[schmookeeg]

I like this choice 1000% more than the skipper for your mission, and I'm a massive Beech snob.

 

[Scott MacMoyle]

I had a skipper and an AA1A. Skipper is a better built and more comfortable plane but its just too darn slow. My AA1A did 6 GPH at 122 MPH. Thats like 20 mpg. I had the autogas STC so it did better than my silverado. I have a Tiger now but all I needed was a 2 seater.

 

[Eric S]

I just bought a 1973 TR-2 (N6516L) last Saturday and flew it from Kansas to Wisconsin.

My version has the 115HP engine STC and standard 22 gallon tanks with the climb prop. On the way home at 2500 Rpm was getting about 112 to 115 Mph at 9500 @ 6.2 Gph.

Was climbing at 600 to 700 fpm down low and 300 to 400 fpm past 6000 and that was with me (250Lbs) and 70Lbs of stuff and full fuel. With me and the old owner for the test flight at pretty much gross was doing 500fpm to 600fpm to 3500, but it was cold so density altitude was -300 when I took off.

Coming from owning a Piper PA-28-235 initially and a Cessna T210F later it is surprisingly light on the controls and actually a lot more fun to fly than I thought, really enjoyed it. The 5.5 XC time was Ok it's reasonably roomy for something so small but would not want to do it too often. But anything up to 2 to 3 hours should be doable.

Anyway if you have more questions pop me a message, though as I said my experience is limited as I'm just getting to know the new guy.

 

[Oldmanb777]

I soloed in a Yankee. there will always be a soft spot for them.

 

[David Baker]

The flap switch is also prone to failure. It sits right under the canopy bow so any water that leaks, leaks right onto the switch. It's an expensive little bugger so operate it several times to make sure it's good. You have to hold it down for the flaps to deploy. When you want the flaps up it will stay in the retract position so you don't have to hold it. There are inspection covers where the gear enters the airframe. There are large aluminum brackets that attach the gear to the spar. Check those for corrosion. The nose spring rod is supposed to be pulled, inspected, cleaned, and greased during the annual but nobody ever does. Lastly check the nose wheel fork for cracks and ensure the bearings are properly pre-loaded so you don't get nose wheel shimmy.

On the flap switch issue, you might check the brush spring within the flap motor. It's threaded into the motor housing via an attached countersunk bolt. It takes some doing, including removal of the passenger seat, but you might check that first before the switch function.

 

[David Baker]

I just made an appointment to go look at one. It has the 1580 pound gross weight and "bigger"34 gallon fuel system, O-235-C2C, and 7157 prop. It is supposed to be a 133 mph, 7 gph airplane with enough range with full tanks, and enough payload for my mission: one 250 statute mile flight about 14 times a month with one 180 pound pilot and 20 pounds of baggage. I also need to be able to carry a 140 pound passenger and another 20 pounds of baggage on an irregular basis.

Midwest USA, O & D airports at about 500 ft AMSL, highest terrain feature about 2000 ft AMSL. 7153 prop is also approved for type-- and was standard on trainer version. "Required" trips will be flown well under gross weight.

Does anyone have first hand or reliable second hand experience with the type?

Any quirks? Or things to look at closely?

Thanks.

The O-235-C2C does not make the little Grumman a Bush Plane. If you manage to get a 133 MPH cruise speed with the TR-2, you must be acquainted with Mr. Lopresti. Wheel Pants help somewhat with cruise figures, but 133 MPH was never achieved during my experience with the plane. 7 GPH is a little high. With the standard fuel tanks, recommended leaning and a little prayer, the Grumman will fly 3 hours to dry tanks. Actually, 2 hours plus a few minutes was my physical limit, with those needed earphones feeling like a vice on my noggin.

 

[David Baker]

These same questions come up pretty regularly on here so a search will answer a lot. I had an original AA1 with the "hot wing". It's an enjoyable airplane to fly. Controls are light and responsive, great visibility and decent room. They can be a little tight on leg room if you are long legged. While they are indeed faster than it's competition, I didn't get book cruise speeds and I don't think most do either. Most are 5-10 kt slower than claimed. It's about the cheapest airplane you could own. The annuals are quick and easy and there aren't a lot of gotchas. There is an AD for routine inspection of the elevator spring cartridge but it's not that expensive to fix. If it doesn't have an oil cooler I would add one. Check the flaps and ailerons for excessive play in the hinges. The fuel sight glasses are prone to leak but it's an easy fix. The only other issue I had was fuel leaks at the wing root. There is a rubber hose that connects the fuel tanks to the airframe that will eventually go bad. They are not easy to replace and require cutting an inspection hole under the wing near the root. If it has an inspection cover there, the hoses have already been done.

These same questions come up pretty regularly on here so a search will answer a lot. I had an original AA1 with the "hot wing". It's an enjoyable airplane to fly. Controls are light and responsive, great visibility and decent room. They can be a little tight on leg room if you are long legged. While they are indeed faster than it's competition, I didn't get book cruise speeds and I don't think most do either. Most are 5-10 kt slower than claimed. It's about the cheapest airplane you could own. The annuals are quick and easy and there aren't a lot of gotchas. There is an AD for routine inspection of the elevator spring cartridge but it's not that expensive to fix. If it doesn't have an oil cooler I would add one. Check the flaps and ailerons for excessive play in the hinges. The fuel sight glasses are prone to leak but it's an easy fix. The only other issue I had was fuel leaks at the wing root. There is a rubber hose that connects the fuel tanks to the airframe that will eventually go bad. They are not easy to replace and require cutting an inspection hole under the wing near the root. If it has an inspection cover there, the hoses have already been done.

 

[David Baker]

Oil temps were one of the first issues I had with the TR2. I tried reshaping the baffling, lower viscosity oil, topping off oil for each flight and finally running auto gas (STC for Low Lead. That cooled the temps down a little.) But until I sold it, the needle was nudging the red line during most flights. When I bought the plane, it had sat for two years in Spokane, WA, and it was part of a probate case, until the late owner's widow consigned it for sale by an FBO. The engine had Zero Hours SMOH, but the overhaul took place before the owner passed away. Maybe it's just a hot little plane all around..

 

[Pinecone]

Have you tried a second sender or gauge>. High reading may not actually be high temp,

I have a number of hours in an AA-1B in Texas (Del Rio), and no temp problems even in the summer

 

[Magman]

It’s possible the time sitting resulted in rust on cylinder walls and pits that wear rings. A low compression reading results in hot gases bypassing the rings and heating the oil in the Case. A differential compression check should be in your near future.

 

[texasclouds]

I don’t know what language y’all are speaking, but you misspelled Cezzna!

 

[David Baker]

Yes it had the stall strips. There was nothing unusual or dangerous about how it stalled. The difference is a Grumman will stall where as most trainers will just mush down with the controls in your lap as long as you are coordinated. In my 150 I could hold the yoke all the way back, you would get a slight drop of the nose followed by a 500 fpm decent. In the Grumman you will get a slight buffet, then the nose will drop and require releasing the back pressure to recover.

I discovered a flight regime that surprised me: Turning final, the plane suddenly dropped from 700 feet AGL to just about zero feet AGL. I'll assume it was a stall/mush, but there was no buffet, wing drop or pitch variation coincident with that drop. The yoke was not full aft, nor was the bank too steep. It just fell out of the sky. I had less than full tanks and myself aboard, so it wasn't over MGTOW or out of the CG envelope. This only happened once, and I went out afterward and practiced stalls until sunset.

 

[David Baker]

Have you tried a second sender or gauge>. High reading may not actually be high temp,

I have a number of hours in an AA-1B in Texas (Del Rio), and no temp problems even in the summer

I didn't install a new sender, though that may have been a factor. I just figured the engine was tight with new cylinders/rings, and would eventually wear in to the point where the temps would be comfortably in the green. I flew it about 180 hours until I sold it.

 

[chemgeek]

This is quite an old thread, but I'll add a reality check for flying the AA-1X. I owned an AA-1A for 4 years and put over 400 hours on it, mostly cross country. The AA-1B has 60 extra pounds of gross weight compared to the AA-1A, but otherwise these are comparable aircraft with the O-235-C2C engine. Realistically, this is a one-person airplane with full fuel and luggage. Most specimens won't be anywhere near the "basic" empty weight, so check actual useful load carefully. While the tanks hold 24 gallons, the usable fuel is 22 gallons. Realistically, you are going to get about 108 kt at WOT with the cruise prop, at about 6 gph. That's how I flight planned, and both speed and fuel estimates were spot-on. Basically, this is a 3-hour airplane MAXIMUM with MINIMUM VFR reserves. My rule was at 3 hours you better be over an airport. That's what my type-specific instructor told me, and he was right. With 2 FAA-standard persons on board and full fuel, there is very little leftover useful load for baggage. If you are above FAA-standard weight, that margin erodes quickly. At MGW, climb is pretty anemic, typical for 2-seat trainers. For one and baggage, it is a reasonable regional VFR XC airplane, with decent climb, and it will outrun most older C-172 models. The O-235-C2C engine is pretty tough and reliable, and the plane is stone-simple to maintain if you have a Grumman-savvy mechanic. I had no major issues with my plane, other than ugly paint. The sight tubes with fuel in the cockpit gave me the willies, but there haven't been many accidents to my knowledge where that was a significant factor in an accident. It's the simplest fuel gauge ever.

I upgraded to an AA-5 Traveler to get more useful load, and not have to operate at MGW. Travelers are quite a bit more affordable than the AA-5A and AA-5B models, have ample engine cooling through the big maw of an air inlet, and use a similarly tough O-320-E2G engine. If you get the high-compression STC (many examples already have it, because it is so desirable) it becomes quite reasonable in climb, and/or faster if you attach a higher pitch STC prop. My model is not the cleanest aerodynamically, but 115-120 kt is achievable in cruise at 8.0-8.5 gph depending on rpm setting, and you can fly 2 and any reasonable amount of luggage and be well below MGW. With the STC engine and prop, I can maintain 500 fpm climb with two aboard and luggage to 10,000 MSL in summer. Endurance with the 37 gal (usable) tanks is a reasonable 3.5 hours with IFR reserves, and I plan for 3 hour IFR or 3.5 hour VFR legs. It shares much of the same, simple maintenance factors of the AA-1 series. Extra performance and fuel margin is a huge safety upgrade for XC flying, especially for IFR.

Both the AA-1A and AA-5 are quite docile to handle with no bad habits. Just fly by the POH. They are not Cessnas. 75-80 mph on final for both models and Bob's your uncle. The AA-1A is a little more sporty in roll with its short wings, and immensely fun with the bubble canopy (and hot in the summer!) but the AA-5 series has much more utility for traveling. In the AA-1A, my wife and I basically joked about the two of us and a shared toothbrush for traveling. (And we were FAA standard weight back then.) The AA-5 is so much more comfortable, and has useful load margin to accept modern avionics as well as a reasonable amount of luggage. We don't have to worry about bringing back stuff in the cargo compartment when making LL Bean trips. (Yes, the AA-5 seats can be folded down to generate a huge, flat bottomed cargo compartment that can accommodate large items. We've had the plane stuffed in back with shopping bags for trips home.)

 

[David Baker]

This is quite an old thread, but I'll add a reality check for flying the AA-1X. I owned an AA-1A for 4 years and put over 400 hours on it, mostly cross country. The AA-1B has 60 extra pounds of gross weight compared to the AA-1A, but otherwise these are comparable aircraft with the O-235-C2C engine. Realistically, this is a one-person airplane with full fuel and luggage. Most specimens won't be anywhere near the "basic" empty weight, so check actual useful load carefully. While the tanks hold 24 gallons, the usable fuel is 22 gallons. Realistically, you are going to get about 108 kt at WOT with the cruise prop, at about 6 gph. That's how I flight planned, and both speed and fuel estimates were spot-on. Basically, this is a 3-hour airplane MAXIMUM with MINIMUM VFR reserves. My rule was at 3 hours you better be over an airport. That's what my type-specific instructor told me, and he was right. With 2 FAA-standard persons on board and full fuel, there is very little leftover useful load for baggage. If you are above FAA-standard weight, that margin erodes quickly. At MGW, climb is pretty anemic, typical for 2-seat trainers. For one and baggage, it is a reasonable regional VFR XC airplane, with decent climb, and it will outrun most older C-172 models. The O-235-C2C engine is pretty tough and reliable, and the plane is stone-simple to maintain if you have a Grumman-savvy mechanic. I had no major issues with my plane, other than ugly paint. The sight tubes with fuel in the cockpit gave me the willies, but there haven't been many accidents to my knowledge where that was a significant factor in an accident. It's the simplest fuel gauge ever.

I upgraded to an AA-5 Traveler to get more useful load, and not have to operate at MGW. Travelers are quite a bit more affordable than the AA-5A and AA-5B models, have ample engine cooling through the big maw of an air inlet, and use a similarly tough O-320-E2G engine. If you get the high-compression STC (many examples already have it, because it is so desirable) it becomes quite reasonable in climb, and/or faster if you attach a higher pitch STC prop. My model is not the cleanest aerodynamically, but 115-120 kt is achievable in cruise at 8.0-8.5 gph depending on rpm setting, and you can fly 2 and any reasonable amount of luggage and be well below MGW. With the STC engine and prop, I can maintain 500 fpm climb with two aboard and luggage to 10,000 MSL in summer. Endurance with the 37 gal (usable) tanks is a reasonable 3.5 hours with IFR reserves, and I plan for 3 hour IFR or 3.5 hour VFR legs. It shares much of the same, simple maintenance factors of the AA-1 series. Extra performance and fuel margin is a huge safety upgrade for XC flying, especially for IFR.

Both the AA-1A and AA-5 are quite docile to handle with no bad habits. Just fly by the POH. They are not Cessnas. 75-80 mph on final for both models and Bob's your uncle. The AA-1A is a little more sporty in roll with its short wings, and immensely fun with the bubble canopy (and hot in the summer!) but the AA-5 series has much more utility for traveling. In the AA-1A, my wife and I basically joked about the two of us and a shared toothbrush for traveling. (And we were FAA standard weight back then.) The AA-5 is so much more comfortable, and has useful load margin to accept modern avionics as well as a reasonable amount of luggage. We don't have to worry about bringing back stuff in the cargo compartment when making LL Bean trips. (Yes, the AA-5 seats can be folded down to generate a huge, flat bottomed cargo compartment that can accommodate large items. We've had the plane stuffed in back with shopping bags for trips home.)

 

[David Baker]

During my ownership experience with the TR2, I never managed 3+hours endurance, no matter how I leaned the little Lycoming. It flew 3 hours to dry tanks, and that was 'demonstrated' on the first leg of my flight to Sacramento (Actually Rio Linda..) from Spokane. The POH was...shall we say...optimistic about fuel burn statistics. As I approached the 2.5 hour enroute time frame, nearing Redmond, Or., she quit running, to my great surprise. I looked at the sight gauge, and there was no fuel indicated. That was the right gauge I referenced. The left one didn't show much gas available, and my only option was to switch tanks, continue toward Redmond, and hope for the best. I made it, but just barely, and that was 2.8 hours from takeoff. From that lesson I learned to ignore the POH data, and watch those gauges.

 

[David Baker]

It’s possible the time sitting resulted in rust on cylinder walls and pits that wear rings. A low compression reading results in hot gases bypassing the rings and heating the oil in the Case. A differential compression check should be in your near future.

I made sure the FBO performed an oil change and Annual Inspection on the TR-2 before I bought it. I don't remember the what compression values read, but they didn't indicate any cylinder issues. The oil screens were checked every 50 hours, and they were clean. The A&E who performed the engine overhaul recommended that the FBO should scope the engines, but that sorta ticked him off. He insisted that the engine was sound. It ran fine, but hot.

 

[David Baker]

These same questions come up pretty regularly on here so a search will answer a lot. I had an original AA1 with the "hot wing". It's an enjoyable airplane to fly. Controls are light and responsive, great visibility and decent room. They can be a little tight on leg room if you are long legged. While they are indeed faster than it's competition, I didn't get book cruise speeds and I don't think most do either. Most are 5-10 kt slower than claimed. It's about the cheapest airplane you could own. The annuals are quick and easy and there aren't a lot of gotchas. There is an AD for routine inspection of the elevator spring cartridge but it's not that expensive to fix. If it doesn't have an oil cooler I would add one. Check the flaps and ailerons for excessive play in the hinges. The fuel sight glasses are prone to leak but it's an easy fix. The only other issue I had was fuel leaks at the wing root. There is a rubber hose that connects the fuel tanks to the airframe that will eventually go bad. They are not easy to replace and require cutting an inspection hole under the wing near the root. If it has an inspection cover there, the hoses have already been done.

Earlier versions were having bonding failures with ailerons, and one AD I received--but it didn't apply--dealt with the carburetor. I had the mixture control replaced with a twist model, and I bought landing lights in bulk. There was a friction knob for the canopy, which wouldn't stay locked (Over Center) with the handle. My most costly fix was the alternator. It popped the circuit breaker, and had to be replaced (Over $800.00 for a Yellow Tagged, Refurbished Model. Turned out it was a standard model you'll find on many cars!)

 

[Eric S]

@David Baker Lol it sounds like you have my planes twin. I have 1973 TR2 and it eats landing lights like candy (I just converted to LED cause I got tired of replacing them.) and my alternator keeps popping the breaker and my A&P is talking about replacing it this annual. At least it sounds like a common problem.

 

[David Baker]

Those alternators cost big bucks. The diagnosis for my 1974 model was a "Flat Spot" on the winding. When I saw the replacement unit, the manufacturer label read "Prestolite". It was exactly like the ones I replaced in the Chrysler cars I owned. I was seriously pondering a purchase of the replacement at an auto parts store, but it had to be yellow tagged. You can view a video of the little Grumman on You Tube. (N8872L) It didn't look like that when I bought it, nor when I sold it. Did you ever see the wings puff up in the heat?

 

[Eric S]

I've got N6516L, and no haven't noticed that yet, but then teh wings on this one were redone by fletchair in 2009 from the logs. I'll definitely keep an eye on wing puffines though.

 

[David Baker]

I've got N6516L, and no haven't noticed that yet, but then teh wings on this one were redone by fletchair in 2009 from the logs. I'll definitely keep an eye on wing puffines though.

It's a good idea to paint the wings with light colors. "Rudolph" (My Grumman had a bright red spinner) was painted medium brown with tan trim. The wings are actually air tight, so when they heat up, the internal air expands. I was surprised to see how the wings would fatten up during warm days. They generally returned to normal after .5 hours of flight.