Glide speeds PA28R versions
 

I have been reading up on the procedures for the Piper Arrow (three different variants actually) and something struck me as odd. If you take a Piper Arrow III (PA28R-201) and compare this to a Piper Arrow IV (PA28RT-201T) then there is a marked difference in best glide speeds: 79 kt for the Arrow III and 97 kt for the Arrow IV. These aircraft both have the newer 'tapered' Piper wing and apart from the engine they should be aerodynamically similar (I'm ignoring the changed position of the stabilator here but still). Anyone with thoughts about the 18 knot difference?

Do the different engines come with markedly different MTOW? glide is (usually) quoted at MTOW.

If I can remember correctly the iv is +- 200lbs heavier

The Arrow IV that I flew was 79kts best glide and it was stated that in the POH.

Best Glide speed on an Arrow I is 111mph (96kts).

Right, so let's summarize:

Arrow I: 111 mph (96 kt)
Arrow II: 105 mph (91 kt)
Arrow III: 79 kt
Arrow IV (turbo): 97 kt

mcgoo is that an Arrow IV with a turbo? If not then it appears that the non-turbo IV matches the III which would make sense. The Arrow I and II share the same 'hershey bar' wing while the III and IV both have the tapered wing. But that brings up the question: why would bolting a turbo to an engine change the glide speed?

As for weights (MTOW), I don't have the Arrow I POH but for the others:
Arrow II: 2650 lbs
Arrow III: 2750 lbs
Arrow IV (turbo): 2900 lbs

Jhieminga

haven't got a POH to hand, but my pilots notes for the Arrow IV (not turbo), say 79kias best glide.

It's all to do with the weight, IMHO...how much extra does the turbo & plumbing weigh? Are there any other things that would cause increased weight? From Wikipedia

"For gliders, a different polar curve exists for the same glider at every gross weight. As the weight increases the polar moves down and to the right and becomes a little flatter, but retains approximately the same shape. Both airspeed and sink rate increase for equivalent points on the curves, but their ratio remains the same. Both heavy and light glider achieve the same best glide ratio, as shown here, but the heavy glider does so at a higher speed. This is the reason for carrying ballast to improve glide performance when the thermals are strong enough, even though the climb rate suffers".

Is it possible that the 9 and the 7 were simply transposed in error? 79 becoming 97

Seems a co-incidence that it's the same two numbers....?

Directly, it would not, however, fitting a more grunty power plant can allow a higher max gross weight which will in turn lead to a higher (quoted) best glide, 'cos when you're heavier you need to go faster.. which was what I pondered with my first post. The magnitude of the difference seems rather high for such an explanation however.

I do wonder, if, as waldo posted there might be some interesting transposition going on.

Otherwise, I haven't a clue.

So do mine.

G

Jhieminga

Yes it was a non turbo.

Interesting discussion. What are the other V-speeds for all these different models?

Best glide is normally a few knots short of Vy. Does Vy differ that much as well?

Sounds ilke digits were transposed.

Our Group Arrow 2 (200HP HersheyBar wing) best glide speed is 105MPH (ASI is in MPH) =91Kt: But 95 MPH (83Kt) over the threshold

The Arrow 4 (non turbo) that I also fly has a glide speed of 79Kt (ASI is in Kt =91MPH)

So the floaty tapered wing Arrow 4 seems to have a much slower best glide speed which fits with the Slab wing Arrow's tendency to drop like a stone with power off.(Which can in fact be a very useful feature on occasions.)

Clear ?(as mud)

Cusco

May have to do with auto gear extension
 

Some of the early arrows have a pitot based gear extension system at about 95mph... if you drop below that the wheels pop down which is seriously going to affect gliding range.

I suspect that may explain the difference...

I doubt it has to do with gear extension - should I have an engine failure you can bet I'll be holding up that gear override if I need to. I also don't think the change in wing loading is enough to explain such a change in best glide speed. I'm going with the transposed digits theory too.

I fly a 1967 arrow-1 with the hershey bar wing and the 180 lycoming. Interestingly enough I cannot find the best glide speed in the POH. Vy is 100mph, which is about what I would use. The best glide in an arrow-1 is still dismal. In normal ops, there is just about no such thing as too high or too fast, once you get the gear & flaps down, power back and RPM up. The engine failure section in my POH advises that the most common cause of engine failure is fuel, and that you should monkey around with the fuel selector, boost pump, and mixture. Apparently if that does not work they think you should give up.

-- IFMU

For a while I had the same thought, but it would be strange for Piper to leave a misprint like that in a POH for so long. I've found graphs for the Arrow IV, both turbo and non-turbo variants so we've got a straight comparison
Non-turbo Arrow IV:
http://www.vc10.net/div/Arrow-S5-26.jpg

Turbo Arrow IV:
http://www.vc10.net/div/TurboArrow-SC5-4-2.jpg

If I use these to work out the glide distance from 10.000 ft for both variants I get 16,5 Nm (1:10) for the non-turbo and 16 Nm (1:9,7) for the turbo, so the performance is almost the same. The difference could be an error on my side.

And to keep things interesting, the first graph shows the glide speed for the non-turbo as 78 kt instead of 79!

Arrow III turbo is also 97kt

Strange huh

Nigel

I've seen exactly the same discussion on piperowner.org some time ago. If I recall correctly, no one could actually really explain why it is 97 for the T-Arrow. Same wing as the non-turbo and roughly the same weight allegedly could not explain the 18kts (!) difference. The theory above about gear override is interesting, but it is the same for the non-arrow so that doesn´t explain it either. I think the discussion ended with 1) the most likely explanation being a typo and 2) that max gliding distance does not change that much with different gliding speed (but the Rate of Descent does) so it´s more a matter of keeping close to Vy and running the checklists, identifying the problem and most importantly look for the most suitable landing spot... Sorry for not being with more help, but I thought I´d share what I read somewhere else on precisely this issue.

I'll third that