Speed Mods - Snake Oil?

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Hengelo

Line Up and Wait
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Hengelo
Does anyone know of a table that lists speed improvements (by type) per component, or am I searching for Atlantis?

In the cycling world it's pretty straightforward to get $/second, I don't understand why aviation is so opaque unless (gasp, where is my fainting couch?) it's all snake oil.

ttchart.jpg
 
Hengelo said:
Does anyone know of a table that lists speed improvements (by type) per component, or am I searching for Atlantis?
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I've never seen an all-inclusive "table" but each vender usually lists what improvements you can expect by installing their mods. Even Cessna made claims of airspeed increases with wheel fairings installed. Plus there's been a number of articles on the topic detailing the various mods.
 
It's also not cumulative (e.g. 2kts from gap seals, 2kts from wheel pants, 2kts from Powerflow exhaust, 2kts from HC pistons, 2kts from etc does not give you 10kts).
 
with a fixed-pitch prop, a given RPM is going to give a particular airspeed regardless of speed mods, right? what would change is fuel efficiency, yes?
 
I looked at a bunch a year or two ago and concluded that they are priced at one amu per knot
 
Capt. Geoffrey Thorpe said:
no.
What is your airspeed during a runup compared with the same RPM in the air?
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conversely, with a cruise prop, what is the airspeed and fuel burn at 75% power vs the same airplane with a climb prop?
 
Don't forget the wax... that's good for like... what 5 kts??

All seriousness... we got ours with flap and aileron gap seals, wingtips... previous owner purchased/installed so I didn't take the purchase hit. Seems to make the Arrow faster than others... trues out at 150 kts in cruise which is faster than some others. Dunno if the speed mods make a difference or not. Maybe it's the grime on the belly or the fancy stripes on the sides...
 
Bob Noel said:
a given RPM is going to give a particular airspeed regardless of speed mods, right?
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But if you reduce your overall drag and clean up the air stream you will get more speed at that same RPM setting. For example, wheel fairings will give you more indicated speed at the same power setting. There are many articles and test details out there that explains it better and in more detail. There have been many routes to take to get more speed without changing the engine or prop over the years.
 
Buyers of these speed mods are highly biased. For instance, if I was to pay 40k for a lopresti cowl, you better believe I'm going to subconsciously skew any test I might perform to make that purchase more palatable.

The best speed mod is a bigger bladder.

Making sure the airplane is rigged properly is a big way to potentially increase speed.

At the end of the day does 10 more knots really make that much of a difference? Less than 30 minutes on an 800 mile trip. Not having to stop to take a leak after 4 hours is probably worth 30 minutes right there.
 
There is no single table that lists all mods for all models. Think about the number of models times the number of companies that do mods and then realize the only table that would matter is the one for your plane.

Do you have a specific model?
 
What plane are we talking about?

I have a 1980 N 172 with a 320 160hp motor. A PowerFlow exhaust is not snake oil at least on my 320 motor. It has been a very worthwhile addition to my plane. Probably does not help it go much faster but definitely helps it climb better. Makes more torque for sure. It is couple kts faster than my buddies 160hp cheerokee. It gives it a very distinct sound, I have been told many times I have the best sounding 172.

A good glaze job also seems to help my draggy 172.
Not that is picture proves anything and the temp was 7°f this day, at 2350 rpm it is going 110kts, has plenty of low torque, IMO.
IMG_1266.JPG
 
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Gary Ward said:
What plane are we talking about?

I have a 1980 N 172 with a 320 160hp motor. A PowerFlow exhaust is not snake oil at least on my 320 motor. It has been a very worthwhile addition to my plane. Probably does not help it go much faster but definitely helps it climb better. Makes more torque for sure. It is couple kts faster.
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It depends….some exhaust systems have already been tweaked by the manufacturer so any improvement is not measurable.
Personally I don’t like how they look on my model, factory exhaust pipe is tucked closed to the body, Powerflows stick out like a sore thumb, any improvement in engine performance is counteracted by the increased drag.
 

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What are we looking at.....? How is that fast? If you want to go fast.....get a faster plane.
Gary Ward said:
What plane are we talking about?

I have a 1980 N 172 with a 320 160hp motor. A PowerFlow exhaust is not snake oil at least on my 320 motor. It has been a very worthwhile addition to my plane. Probably does not help it go much faster but definitely helps it climb better. Makes more torque for sure. It is couple kts faster than my buddies 160hp cheerokee. It gives it a very distinct sound, I have been told many times I have the best sounding 172.

A good glaze job also seems to help my draggy 172.
Not that is picture proves anything and the temp was 7°f this day, at 2350 rpm it is going 110kts, has plenty of low torque, IMO.
IMG_1266.JPG
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Years ago, I had a Cherokee 180D. Got wheel pants, flap and aileron seals, wing root kit. When it was all done, I regularly got 124ktas out of it. Everyone else I've talked to with one said they never got that sort of speed. It wasn't the top end that I got the big performance increase though. The stall speed dropped considerably. Take off and landing distances ended up way less than book due to the drop of Vs.
 
Gary Ward said:
OK your right, Not Fast.
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Pretty plane.....but, it's never gonna be a C-210.

And as much as I wanted my Cherokee Six to go faster....It was never gonna be much faster without big changes. At some point you'll realize what you have....and what you don't.
 
Checkout_my_Six said:
Pretty plane.....but, it's never gonna be a C-210.

And as much as I wanted my Cherokee Six to go faster....It was never gonna be much faster without big changes. At some point you'll realize what you have....and what you don't.
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For sure, I agree. fast, faster and 172 should never used together. lol

My buddy had a PA24-140 160 STC that we flew together with. He recently sold it and got a arrow II that I have been flying. So I got to experience a little faster plane. I really don't go anywhere with my plane, so it suits my budget and needs for now. Even more so now that gas is way up there in cost.
 
Half Fast said:
Check your w&b. If you can fly with the CG closer to the aft limit you’ll pick up a little speed. Tossing a sandbag or water jug into the baggage compartment is about the cheapest speed mod you’ll find.
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I have a big survival kit, tools, parts, even an axe, water, pots and pans, and firewood in the back. :)
51 lbs of trim balance
 
Checkout_my_Six said:
Pretty plane.....but, it's never gonna be a C-210.

And as much as I wanted my Cherokee Six to go faster....It was never gonna be much faster without big changes. At some point you'll realize what you have....and what you don't.
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You’ll never win the Kentucky Derby with a Jack Axx
 
Half Fast said:
Check your w&b. If you can fly with the CG closer to the aft limit you’ll pick up a little speed. Tossing a sandbag or water jug into the baggage compartment is about the cheapest speed mod you’ll find.
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The second is to lose weight. It seems to me that I always go 2-3 knots faster on the last few gallons vs the first few gallons of a full tank.
 
I deleted a post since someone already made the 'cumulative' reference above..


We have an absolute grab bag of various aircraft in our club.. across 98 planes we have just about every combination you can expect of Cherokee and Skyhawk (plus a few others) in various degrees of barely legal to fly to extremely over improved..

Having flown about 30 of them in the last 5 years I can tell you that the only things I consistently find beneficial are wheel pants

And for one reason or another some planes just seem to fly better... rigging?

We have two 182RG.. oddly enough the over improved one is the one that trues out about 5 to 7 knots slower and climbs about 200 ft per minute less than the other one and generally just does not feel as 'tight'



Does a flop Gap seal help? Sure, probably a little. But I would take any of these improvements holistically and with a big grain of salt
 
You have to compare mods on the same plane. Or compare the two planes before any mods to make sure they are the same.

With the two 182RGs mentioned, one could have a worn cam and making less than full power.
 
I agree with the bigger bladder statement! That and carry more fuel and money.

When I was shopping for planes I wanted fast just like everybody else. What I realized is that there is a delta between speed, payload and range that you have to identify for you mission.

If your normal mission makes you have to stop every 2 hours to fuel up (because you reduced fuel to carry more stuff) then it does not matter how fast you are going as you are going to lose time overall.

For my "mission," I started off flying a friends Arrow that has a TAS of 125kts on average. With 4 adults we could not take a lot of fuel so I had to stop for fuel at least once during the outbound leg which added approximately 45 minutes to an already 2.8 hour trip. One way was now at least a 3.8 hour trip.

I found a Cherokee 6 that could haul what I needed and had the range to fly without stopping. It's TAS was 135kts and an added benefit was I had enough fuel to fly back to my return fuel stop so I save $$ there. My one way trip was now 2.5 hours but I found that the winds were not always favorable so it was more like a 2.8 hour trip. Still I saved an hour one way.

Eight months ago I moved from the Cherokee 6 to a Cessna 310. With my TAS now I can cover that same flight in 1.8 hours. Just don't ask me about the costs...

YMMV
 
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k9medic said:
I agree with the bigger bladder statement! That and carry more fuel and money.

When I was shopping for planes I wanted fast just like everybody else. What I realized is that there is a delta between speed, payload and range that you have to identify for you mission.

If your normal mission makes you have to stop every 2 hours to fuel up (because you reduced fuel to carry more stuff) then it does not matter how fast you are going as you are going to lose time overall.

For my "mission," I started off flying a friends Arrow that has a TAS of 125kts on average. With 4 adults we could not take a lot of fuel so I had to stop for fuel at least once during the outbound leg which added approximately 45 minutes to an already 2.8 hour trip. One way was now at least a 3.8 hour trip.

I found a Cherokee 6 that could haul what I needed and had the range to fly without stopping. It's TAS was 135kts and an added benefit was I had enough fuel to fly back to my return fuel stop so I save $$ there. My one way trip was now 2.5 hours but I found that the winds were not always favorable so it was more like a 2.8 hour trip. Still I saved an hour one way.

Eight months ago I moved from the Cherokee 6 to a Cessna 310. With my TAS now I can cover that same flight in 1.8 hours. Just don't ask me about the costs...

YMMV
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Great post!

For me, it has to have room to carry a large cooler and gear, land and take off from 1000' grass strips, plenty of fuel range to fly out to a remote area, land, and make it back home with adding fuel, because there is no place to buy any. Last week I did over 2 hours Monday, over 4 hours Tuesday, almost 6 hours Wednesday, and Thursday took some friends up for a sight seeing flight, which including landing on a lakeshore, with the tire feet from the water.
 
I have nearly every LoPresti speed model installed on my Comanche. Thank you previous owner. If the mods were cumulative, I'd have a 200kt airplane. Sadly, they aren't. I get about 165kts true, vs. 155 for an unmodded airplane. Climb is some better because of the 3 blade, but it costs a little speed. The only mod I don't have are wing root seals, which aren't really speed related but do help with cabin noise. Would I have spent the money? Heck no.

She is a head turner though. I get lots of positive feedback on the ramp.
 
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