Aft Body Strakes on twin Cessnas??

[N747JB]

Any real world experience with these?
http://www.aircraftstc.com/10products/22400-series/400-information
They claim 4-7% increase in cruise speed, well that's 10-17 knots for a 425 and 8-15 for a 421. A little pricey, like most speed mods $1000 per knot, but I am curious if anyone has actually flown with them and has any data to back up the speed and climb increases? I understand the testimonials, but I'd like to know from someone else's point of view.

 

[kgruber]

They seem to be successful on King Airs. Google Jim Raisbeck.

 

[N747JB]

They seem to be successful on King Airs. Google Jim Raisbeck.

I've seen them on KA's but I've never heard much about speed increases only you can legally fly without the yaw damper to certain altitudes.
I don't have a yaw issue, but I would like 12-15 knots, but I'd be disappointed if I got 3-4!!

 

[Norman]

Having installed lots of "speed mods" on various aircraft with little result I'd be inclined to "Let Mikie try it".

 

[Ken Ibold]

Having installed lots of "speed mods" on various aircraft with little result I'd be inclined to "Let Mikie try it".

I bought a straight tail Lance with all the speed mods already on it. LoPresti cowl, aileron and flap gap seals, wing fillet modifications, "speed" hub caps, cowl/windshield fairing, I forget what else. Based on the manufacturers claims, that thing should have been 20 kts faster than stock. It was maybe 5 knots faster (at most) than the same year straight tail Lance I'd had earlier.

The LoPresti cowl did help engine cooling a little. And the gap seals helped low speed handling a little.

 

[Norman]

I bought a straight tail Lance with all the speed mods already on it. LoPresti cowl, aileron and flap gap seals, wing fillet modifications, "speed" hub caps, cowl/windshield fairing, I forget what else. Based on the manufacturers claims, that thing should have been 20 kts faster than stock. It was maybe 5 knots faster (at most) than the same year straight tail Lance I'd had earlier.

The LoPresti cowl did help engine cooling a little. And the gap seals helped low speed handling a little.

And with that cowl you probably are getting charged more at oil change time. Nobody likes having to undo all those screws. Low man in our shop got that job.

 

[Ken Ibold]

And with that cowl you probably are getting charged more at oil change time. Nobody likes having to undo all those screws. Low man in our shop got that job.

I would show up with a screw gun when I dropped it off. My mechanic was a one-man show.

 

[Ted]

I haven't flown with them, however on the Twin Cessna forum a number of people have them. The reports are mixed but generally positive, anywhere between actually seeing the claims and seeing no speed improvement but still seeing the handling improvements. My guess is that some of it has to do with the experience and skill of the shop installing them. So if you put them on the Conquest, go to a shop that's done more than one.

 

[RotorAndWing]

Speed mods are proportional to the TAS of the airplane being modified.

That's why it's funny to see a sub 250 knot TAS airplane with winglets. Other than looks it doesn't do a hell of a lot for it.

I would imagine the strakes are more to do with stability than speed.

 

[N747JB]

I guess I should have titled the thread "Has Mikie tried the twin Cessna Aft body strakes"
I'm looking for Mikie!

Having installed lots of "speed mods" on various aircraft with little result I'd be inclined to "Let Mikie try it".

 

[N747JB]

Spoke to a guy today that had them installed a couple months ago, he said they are getting 2-400 FPM better climb rates and 6-7 knots indicated airspeed at FL230. So roughly 9-10 knots TAS increase, he has same engines and props that I do. Works out to $1500 per knot.

 

[Fearless Tower]

Speed mods are proportional to the TAS of the airplane being modified.

That's why it's funny to see a sub 250 knot TAS airplane with winglets. Other than looks it doesn't do a hell of a lot for it.

I would imagine the strakes are more to do with stability than speed.

That's good to know, especially since they want over $15k to install winglets on a Baron. I think that will be one mod I'll pass on.

 

[bnt83]

That's good to know, especially since they want over $15k to install winglets on a Baron. I think that will be one mod I'll pass on.

Bout like the $15k carbon cowl for the C177RGs.

 

[N747JB]

That's good to know, especially since they want over $15k to install winglets on a Baron. I think that will be one mod I'll pass on.

I think RAM wants $42K for winglets on a 414A/421C! But they do look cool!

 

[JimG.]

Spoke to a guy today that had them installed a couple months ago, he said they are getting 2-400 FPM better climb rates and 6-7 knots indicated airspeed at FL230. So roughly 9-10 knots TAS increase, he has same engines and props that I do. Works out to $1500 per knot.

Yeah but…

You can “fudge” a little on that 9-10 knots TAS by saying that the increased climb rate gets you to altitude at higher speeds faster…

And…

That $1500 per knot is only on the 1st flight.

After that… the speed increase is free.

(My CPA as always rolled his eyes at my creative accounting by the way)

 

[N747JB]

I think you and my dad went to the same math school!! He can justify ANY expense, it just takes creative thinking. Reminds me of government economics!
And of course if you climb faster, you burn less fuel in the climb to higher fuel saving altitudes! I think you're on to something!!

Yeah but…

You can “fudge” a little on that 9-10 knots TAS by saying that the increased climb rate gets you to altitude at higher speeds faster…

And…

That $1500 per knot is only on the 1st flight.

After that… the speed increase is free.

(My CPA as always rolled his eyes at my creative accounting by the way)

 

[JimG.]

I think you and my dad went to the same math school!! He can justify ANY expense, it just takes creative thinking. Reminds me of government economics!
And of course if you climb faster, you burn less fuel in the climb to higher fuel saving altitudes! I think you're on to something!!

There you go…

Just make it easier to write that check.

Actually… if you put it on your American Express, you get rewards points and air miles…

 

[J3 Driver]

For the 200-400 FPM climb rate increase I'd do it. Bet it helps single engine too.

 

[N747JB]

For the 200-400 FPM climb rate increase I'd do it. Bet it helps single engine too.

It's supposed to help the single engine performance as well, they don't make any specific claims like VG kits, but they are supposed to be "better" or in FAA speak, not worse than originally certified.

 

[Ted]

The climb rate I think would be the biggest issue on the piston Twin Cessnas, probably helps higher altitude ops more significantly.

 

[J3 Driver]

Yeas the only time I had the 421C I used to fly at 25000 it definitely wasn't happy up there. It did it but I don't think she liked it.


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[Ted]

Yeas the only time I had the 421C I used to fly at 25000 it definitely wasn't happy up there. It did it but I don't think she liked it.

Part of that is also the engines. Turbos are working really hard that high. Turbo pistons seem to be the happiest in the lower flight levels.

 

[Skylane81E]

That's good to know, especially since they want over $15k to install winglets on a Baron. I think that will be one mod I'll pass on.

If they are like the Colemil tips on out Navajo you would probably get more from the increase in span than the winglets

 

[Ted]

If they are like the Colemil tips on out Navajo you would probably get more from the increase in span than the winglets

Yeah, but I did find the Colemill tips on the Navajo worked.

 

[RotorAndWing]

Yeah, but I did find the Colemill tips on the Navajo worked.

I had a Panther conversion Navajo, and personally I hated the wing tips. They stiffened the ailerons significantly and I didn't notice that much performance improvement over the stock. Mine was a 325CR converted and had the 350hp engines, short fuselage.

Interestedly, back flying the 727's we had a few converted with the Dugan mod which added winglets. Those airplanes had the same problem with the stiffened ailerons, not much fun to fly. They took a great airplane and made it handle bad.

 

[Ted]

I had a Panther conversion Navajo, and personally I hated the wing tips. They stiffened the ailerons significantly and I didn't notice that much performance improvement over the stock. Mine was a 325CR converted and had the 350hp engines, short fuselage.

Interestedly, back flying the 727's we had a few converted with the Dugan mod which added winglets. Those airplanes had the same problem with the stiffened ailerons, not much fun to fly. They took a great airplane and made it handle bad.

Interesting data point. I flew the PA-31-310 with winglets (short fuselage, no wing lockers), and the PA-31-350 (Chieftain, so long fuselage and wing lockers, had VGs). I didn't notice an appreciable difference in aileron characteristics between them. Overall I found the 310 to be a significantly better performer in takeoff and climb, but in cruise they were pretty even.

 

[N747JB]

I usually kept my 421B in the mid to upper teens, I got her up to FL220 once and she told me she like FL180 better!

Yeas the only time I had the 421C I used to fly at 25000 it definitely wasn't happy up there. It did it but I don't think she liked it.


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[tonycondon]

we took the 421B to FL250 about once a month. you could tell you were in thin air. the turbos and the airplane were happier lower.

the comments about winglets degrading handling are interesting as everything that i've heard about sailplanes is that adding winglets tends to improve roll response and aileron effectiveness, not the other way around.

 

[Skylane81E]

Interesting data point. I flew the PA-31-310 with winglets (short fuselage, no wing lockers), and the PA-31-350 (Chieftain, so long fuselage and wing lockers, had VGs). I didn't notice an appreciable difference in aileron characteristics between them. Overall I found the 310 to be a significantly better performer in takeoff and climb, but in cruise they were pretty even.

I really can't compare, I have flown another chieftain but it has been a while and they have more performance than anything else I've flown.

 

[Ted]

The highest I took the Navajo was 17,500. With no intercooler, it wasn't happy. 14k was really the highest it was happy at, but I could get 200 KTAS on about 38 GPH ROP.

The RAM T310R we had up to FL200. It was happy there, even on a hot day, but I do think it was happier around 180.

 

[JimG.]

The highest I took the Navajo was 17,500. With no intercooler, it wasn't happy. 14k was really the highest it was happy at, but I could get 200 KTAS on about 38 GPH ROP.

The RAM T310R we had up to FL200. It was happy there, even on a hot day, but I do think it was happier around 180.

My 340 had intercooler's, so temperatures were never an issue, but it was happiest between 15,000–180.

And I could keep the cabin below 10,000 at cruise settings where I got the best “miles/gallon”

Any higher took higher manifold pressures and increased fuel flow without picking up much speed to offset it

 

[J3 Driver]

Yes the 421c I flew seemed happiest about 17-18K. I only went to FL250 to clear some weather. I miss that airplane. It was a nice quiet comfortable airplane to fly and with the training link gear it made you look like a pro.

We since sold it and upgraded to a C441.

 

[Ted]

My 340 had intercooler's, so temperatures were never an issue, but it was happiest between 15,000–180.

And I could keep the cabin below 10,000 at cruise settings where I got the best “miles/gallon”

Any higher took higher manifold pressures and increased fuel flow without picking up much speed to offset it

Whether or not you have intercoolers, the induction air temp still will increase as you go higher. Turbo is working harder, which means it's robbing more power from the engine, and is eventually running out of its ability to create boost. The higher manifold pressures and increased fuel flow you saw at higher altitudes were a function of that.