Adjusting Washout

[smmilke]

I have been trying to figure out why my 12D-4-85 is so slow and I'm starting to suspect the rigging of the wings. I have a 71-40 prop, 85 hp, 894# empty and at 2350 rpm only cruise at 80 mph! (Yes, I've verified this with gps and accounted for wind.) From numbers posted on the forum this seems slow even for a similar setup on floats.

I noticed that one wing is washed all the way out and the other is washed all the way in. The plane is just slightly right wing heavy but almost not enough to notice. The ailerons seem to be just above the trailing edge of the wing in level cruise. I've read through the service manual and several threads on this forum but I still have a couple questions.

Do I need to make any adjustments to the jury struts when changing the washout, if so, what is the proper procedure? Are there any tricks for getting good measurements in spite of the rib stitching sticking out and preventing the level from sitting flush with the rear spar? Will changing the washout significantly affect the rigging of one or both ailerons? Finally, does it seem reasonable that I'm losing 15 mph to poor rigging?

[Pearson]

Re: Adjusting Washout

Mike,

The washout might cost you a few mph. But it isn't going to slow you down 15-20 mph. You might want to check the TCDS for your plane, or ask others, to see what prop is supposed to be on it. Also, see if there is something you can do to reduce your empty weight.

[astjp2]

Re: Adjusting Washout

If your prop was 75" then you still would have a climb prop, you are either too short or too flat, the 68" Is like a 48-52" pitch, the 72 should be around 45-50" ish depending on if Mac or Sen...Borrow another prop and see what happens. also your washout should be 1 5/16" at the outermost full rib, with MINOR variations based on how it flies. I can take my hands of the yokes and fly wings level with only rudder input for 20-30 minutes at a time if the winds are calm. THe only way you would have that much difference is if your struts are different lengths...if not, I would set back to factory specs and start over, 1/2 turn at a time until it flies well...1/2 out on one, 1/2 in on the other until it flies wings level with typical load (pilot, survival kit, etc.) Tim

[otrcman]

Re: Adjusting Washout

I'm with astjp2 on this one. The prop pitch and diameter are suspicious. Without even trying another prop, here's a test for you:

What is your fuel usage at cruise ? Fuel flow is a somewhat direct indicator of horsepower. If your prop is too flat, you will be showing a reasonable cruise RPM on the tach, but not making a whole lot of horsepower. As an example, your C-85 at 65% power should be using around 4.7 GPH. If you are using significantly less than that, then you simply aren't making the horsepower and as a result your speed will be down.

The answer to the problem would be to increase prop pitch or diameter to raise your manifold pressure at cruise RPM. But let's not jump to any conclusions until you tell us what your fuel flow rate is at cruise.

Dick

[otrcman]

Re: Adjusting Washout

I'm with astjp2 on this one. The prop pitch and diameter are suspicious. Without even trying another prop, here's a test for you:

What is your fuel usage at cruise ? Fuel flow is a somewhat direct indicator of horsepower. If your prop is too flat, you will be showing a reasonable cruise RPM on the tach, but not making a whole lot of horsepower. As an example, your C-85 at 65% power should be using around 4.7 GPH. If you are using significantly less than that, then you simply aren't making the horsepower and as a result your speed will be down.

The answer to the problem would be to increase prop pitch or diameter to raise your manifold pressure at cruise RPM. But let's not jump to any conclusions until you tell us what your fuel flow rate is at cruise.

Dick

[flyguy]

Re: Adjusting Washout

I have an almost identical aircraft, weight and everything matches, except prop pitch. I always felt mine was slow with the 46 I have, but it IS quite a bit faster than that. I can get close to 80 at 2000 RPM. I don't think it has much to do with your wing setup as I have tried all kinds of weird tricks with the adjustments on mine. Didn't make much difference, except to change the way it flew.

As stated above 45 to (50?) should be much better for cruise. You're running in second gear with the prop you have now. What is your max climb rate now?

DC

[astjp2]

Re: Adjusting Washout

a 70/40 McCauley prop is for a continental A-80 so they could get 2700 rpm with only 80 hp....Tim

[smmilke]

Re: Adjusting Washout

Thanks for the advice guys! My fuel burn at 2350 is 5.2 gph and this results in about 80 mph cruise on wheels, a little slower on skis. I don't have any good numbers for rate of climb, but somewhere in the neighborhood of 500 fpm. I will see if I can borrow a different prop and I'll let you guys know what I come up with. BTW the purpose of all this is to get a little more speed out of a bush plane, I'm not interested in putting on a short cruise prop just for the sake of going faster.

[otrcman]

Re: Adjusting Washout

Your fuel burn sounds just about right at 5.2 GPH. So you are probably making the right horsepower. The prop could still be the culprit, though. It may be so short and flat that it's not running at an efficient point. How is your climb ?

Dick

[otrcman]

Re: Adjusting Washout

Your fuel burn sounds just about right at 5.2 GPH. So you are probably making the right horsepower. The prop could still be the culprit, though. It may be so short and flat that it's not running at an efficient point. How is your climb ?

To clarify what I'm suggesting, here are some engineering terms to consider:

Shaft Horsepower (SHP) = The horsepower delivered at the crankshaft, measured by a dynamometer.

Thrust Horsepower (THP) = This is the actual power delivered to the airframe in flight.

Propeller Efficiency = The efficiency with which the propellor converts shaft horsepower to thrust horsepower.

Simply put, THP = SHP X Prop Efficiency

By measuring your fuel flow, we have pretty much determined your SHP. But because your plane seems slow, it's possible that the prop isn't converting SHP to THP effectively. Props are usually about 80% efficient, give or take a little. If your prop is less efficient, then your Thrust Horsepower will be down.

Dick

[astjp2]

Re: Adjusting Washout

Are you at Chena? If so, find George and see what he can do to help. Everyone around there knows George with the taylorcraft...Tim

[flyguy]

Re: Adjusting Washout

I would suggest that you get a rate of climb indicator installed, even temporarily, before you take that prop off, and check your rate of climb. Bet you it is a lot more than 500 ft/min with that prop. I have a 71 or 72 x 46 (I believe) and I get 850 ft/min consistently at medium temperatures. Then compare the ROC with the changed prop. You may want to go back to slow. It is always a tradeoff.

That prop might turn out to be really good for best angle climb out situations. Just thinkin'.
DC

[astjp2]

Re: Adjusting Washout

Too short for a good climb prop, he would want a 74" diameter with that pitch...I like a 74/42ish and can climb as good as a 150 cub...Tim

I would suggest that you get a rate of climb indicator installed, even temporarily, before you take that prop off, and check your rate of climb. Bet you it is a lot more than 500 ft/min with that prop. I have a 71 or 72 x 46 (I believe) and I get 850 ft/min consistently at medium temperatures. Then compare the ROC with the changed prop. You may want to go back to slow. It is always a tradeoff.

That prop might turn out to be really good for best angle climb out situations. Just thinkin'.
DC

[smmilke]

Re: Adjusting Washout

I may be able to borrow a ROC indicator and temporarily install it, I'll be sure to do so if I can find some other prop(s) to try out. I'm pretty happy with the climb as it is, I can still climb pretty well at 10K ft near gross. It does sound like a longer prop at this pitch would be more appropriate though.

I've heard of people flying with 74'' props but the TCDS for the BC12D-4-85 and model 19 seem to limit length to 72'' or give no limits, respectively. Are 74'' props legal for those models?
I would at least like to fix the slight right wing heaviness, can someone answer the washout/jury strut question?
Has anyone ever come across a straight flying airplane with the wings washed out to the limits in opposite directions? This seems pretty strange as it has never really been in an accident.

[Hank Jarrett]

Re: Adjusting Washout

I have had a passenger actually hold a ROC in their hands while flying. It ides not have to be mounted and in a Taylorcraft the cabin pressure is pretty close to static. Not perfect for an altimeter, but pretty good for a ROC.
As for the wing rigging, you REALLY need to measure the change in angle along the span to know what is going on. I have seen fuselages where the attach lugs were out and one whole wing was at a different angle than the other. It was trimmed out by twisting the wings and at different speeds there was different wing heaviness! On "T" wing you could even have one wing with the ribs on the spars at different angles. There is a little play with the gap at the top and bottom of the ribs. If you have a protractor level you can do a quick check from one side to the other at each rib without even leveling the plane. You are interested in if there is a DIFFERENCE from side to side, not the actual angle for this. If both wings have the same angle at each rib (they WON'T!) there is something else going on. I am betting one wing is actually at a different angle than the other.
Finding the problem is the first step and for that you need to measure the angles. FIXING the problem is a whole different thing. Right now we don't know what to fix.
Measure the angle of the bottom of each rib and the matching rib on the other side first. That will help define the problem.

Hank