Flight Problem Sig Skybolt

[mcnamajp]

I have a Sig Skybolt with an O.S. 90 4-stroke turning a 14-8 Master Airscrew prop. I bought the plane pre-built years ago. The problem I have is when the plane is trimmed for straight and level at low throttle it requires slight down elevator also when full throttle is applied at this same trim it climbs out HARD. - the CG appears to be conservative nose heavy with no fuel about 1/8" in front of leading edge of lower wing. The motor seems to be pointed slightly down from fuselage center-line (not sure why this should be trimmed down to begin with but) should I increase the downward angle on the motor mount?. What can be causing this... I'd like to understand the aerodynamics of it all. Thanks in advance for your advice!

[EJWash1]

Here's page 4 and 35 of the Building and Flying Instructions manual.

Page 4 includes the firewall installation and talks about thrust line deviation. Page 35 includes C.G. range.

Measuring the plan, the C.G. placed at 1/8" forward of the lower wing puts you exactly 5/8" ahead of the upper wing's rear strut fairing, which is depicted on page 35 as the "test flying balance point." The "regular" balance point is 1/4" aft of the lower wing's leading edge.

You may want to look at the engine's thrust angle mounting. This model was offered before the larger 4-strokes were available. Even the box only lists engine size as ".60". I included 2 pics of the engine mounts. The measurement from the front of the firewall to the back of the spinner is 4-1/8". I wonder if the installation of the .90 pushed the nose moment forward? C.G. is C.G., but if there is any up/down thrust added, that may explain exaggerated Pitch up/down with power changes.

Please post what you find as I plan to use an OS Surpass .91 in my Sig.

Hope this helps,

EJWash

[EJWash1]

I became curious about the .91 Surpass in the Sig Skybolt, so I pulled it out and measured it against the plans. I left about 3/32 -1/8" clearance behind the rear-mounted carb (the most rearward protruding item on the engine). The back of the spinner plate moved forward 7/16" from the plans. I take it that yours did the same, unless the builder moved the firewall back. May this have some effect on your pitch -vs- trim situation?

EJWash

[mcnamajp]

Wow, thank you for the effort in your two posts. I appreciate your time taking photos and all. I don't have the prints since I didn't build the plane. I believe I can see a visible down thrust angle on the engine mount but have yet to measure it. I think from the plans that you posted it seems to show zero off axis thrust - is that what you see indicated as well? I know that sometimes down thrust is used but WHY? Shouldn't the motor pull straight and true on axis or is it an effect of extra thrush wash on the lower wing? One thought I had was tweaking both ailerons "UP" (sort of the opposite of flaps) to decrease the positive lift on the lower wing? Any thoughts on what the effects of that would be (the plane doesn't roll nice already cork-screwy). So do you think down thrust/more down thrust is the answer? What do you mean by thrust moment? I'll try to tell if the firewall was moved but I don't think so.... I'll also check the clearannce on the )O.S. FS 91S - yes that is the motor I have installed. Will be pulling the cowl off and get back to you!. Thanks!

[mcnamajp]

I see...it sunk in... the plane of the prop is moved forward on my plane by 7/16"... I'll measure it up to confirm... Why would that change the way the plane flys? again - shouldn't a straight pull forward - pull the plane straight forward? I keep thinking that it's the increase of speed of the plane and the additional prop wash that is changing how the plane pitches at different speeds. EJ since you have the Skybolt plans, I assume you have/had the plane - Did you notice big pitch changes with power applied?

[EJWash1]

Taking the pics are a nonevent, and you're welcome.
I see...it sunk in... the plane of the prop is moved forward on my plane by 7/16"... I'll measure it up to confirm...
Keep in mind that the 7/16" is what I came out with when I placed the .91 atop the plans. Measure from the front of the prop plate (back of the spinner plate) and post that measurement. I'll compare it to the plans.

Why would that change the way the plane flys? again - shouldn't a straight pull forward - pull the plane straight forward? I keep thinking that it's the increase of speed of the plane and the additional prop wash that is changing how the plane pitches at different speeds.
Power can change the plane's attitude. An increase in thrust (speed) will increase lift. It is more noticeable in some aircraft than others.

The fact that the 4-stroke weighs more pushes the C.G. forward, which has to be compensated for, and the fact that the engine is now (in your case, maybe) forward of the planned location has to be compensated for.

There is a question about biplane C.G. here (http://www.rcgroups.com/forums/showthread.php?t=1026940) in another thread. One respondent recommends 3 degrees right thrust and 3 down thrust. The right thrust is for engine torque, and I'm not sure of the reasoning for the down thrust.

EJ since you have the Skybolt plans, I assume you have/had the plane - Did you notice big pitch changes with power applied?
When I reentered the hobby a little more than a year ago after a twenty-plus year hiatus, I collected several kits and plans. I have two Sig Skybolts in the box. I haven't flown this before, but flew an Andrews Aeromaster for several years. A little shorter on dimensions, but had the same configuration: longer, swept top wing and a shorter, straight bottom wing. I do remember adding in down thrust, but I no longer have the plans or the airplane, so I can't make a comparison.

Wait and see if more flyers chime-in on this that have more experience. In the meantime, you may want to try more down thrust by placing a washer under the rear mounting bolt of the engine.

EJWash

[mcnamajp]

EJWASH to answer some things you raised trying to answer my questions... :) The O.S. Carb on my 91 has a flapper plate over the carb inlet (what is that for) as mounted the hinge of that plate is just a little under 1/8" off the firewall this places the back of the carb as you have measured to be about .43" off the firewall. The front of the spinner plate I have mounted is measured to be 5" off the firewall. - this is well forward of what the plan shows. I think your print photos put the prop plane at about 4 3/16" off the firewall - so presently my prop plane is 13/16" farther out than the plan shows - that's quite a difference but I'm not sure what it means???
There is about .2" of down thrust in the motor in the pitch plane. I did eyeball this with a dial mic but it is definitely more than 1/8". I measure from back plate of motor to front of spinner plate to be 3.65" in that distance the downthrust meaured is (best est.) .2" this is 3.1 degrees. I tried to show this in the photos. The wooden ruler aligned with the motor centerline definitely shows the significant down thrust. I tried to mock up the print thrust line with the clear ruler and estimate the down pitch.. Given the configuration of the motor mount I guess I'd have to shim or grind the mount to increase this - what would you suggest and how far would I go? Should I go to 5 or 6 degrees off axis? Five degrees would make that .2" measurement become .31"; at 6 degrees .38" :eek: Also if I grind the motor mount I could put that pivot point for the flapper plate on the carb right against the motor mount moving the prop plate to 4 and 7/8" from the firewall. Does it seem that a motor with this much downthrust 3 Deg (already) would make the plane climb like a rocket even with slight down elevator trimmed in and a slightly forward CG???
Well... even at low throttle I have to trim in some down elevator - when the motor quits I have to change to "up" elevator to keep from flying into the ground. So even though 3 deg seems a lot, more is needed -I guess. What is the down side of too much down thrust?
Was the recommended .60 size engine a 4 stroke or a two stroke? A .91 four stroke compared to .60 four stroke would be 50% more power I'm not sure how the .91-4 would compare to a .60 two stroke for power??? I seem to remember someone saying a .90 4 stroke is about equal to a 60 two stroke??? A thought... if the motor IS over-powered for the plane? , the plane is flying faster at full throttle than design speed, as you say - therefore there is more lift and the plane would tend to climb? - do you think the additional prop wash over the wings especially the lower one is also a big factor?... I mention this because as I increase down thrust on the engine the angle of attack between the wing(s) and the prop wash will increase thereby increasing whatever lifting effect there is. To give a measure of power - this motor at full throttle held vertical will almost give 1 to 1 thrust/weight, it's very light in your hands.

[EJWash1]

The O.S. Carb on my 91 has a flapper plate over the carb inlet (what is that for)
That's a choke valve. Earlier 4-strokers had them to draw fuel into the engine. Newer engines do not come with them. If you have an electric starter or a well-tuned and broken-in engine, you don't need to choke the engine before starting it. If there's no linkage connected to it to manipulate it, you can remove is if your want.
...as mounted the hinge of that plate is just a little under 1/8" off the firewall this places the back of the carb as you have measured to be about .43" off the firewall. The front of the spinner plate I have mounted is measured to be 5" off the firewall. - this is well forward of what the plan shows. I think your print photos put the prop plane at about 4 3/16" off the firewall - so presently my prop plane is 13/16" farther out than the plan shows - that's quite a difference but I'm not sure what it means???
The big thing in using a heavier engine, or extending an engine forward is C.G., but you've already determined that you're within C.G.. I can't think of another factor in terms of what you're experiencing with the thrust/pitch/trim situation. I initially brought it up in consideration of C.G..
There is about .2" of down thrust in the motor in the pitch plane. I did eyeball this with a dial mic but it is definitely more than 1/8". I measure from back plate of motor to front of spinner plate to be 3.65" in that distance the downthrust meaured is (best est.) .2" this is 3.1 degrees.
I haven't seen more than 3-4 degrees of right or down thrust, which is plenty. I would not increase the down thrust in your case.
Does it seem that a motor with this much downthrust 3 Deg (already) would make the plane climb like a rocket even with slight down elevator trimmed in and a slightly forward CG???
NO. The problem has to be somewhere else.
Well... even at low throttle I have to trim in some down elevator - when the motor quits I have to change to "up" elevator to keep from flying into the ground. So even though 3 deg seems a lot, more is needed -I guess. What is the down side of too much down thrust?
This is a clue that other areas have to be checked.

In looking at your pictures, you can see that the builder did not follow the plans for the cabane (sometimes referred as the "ca-pain"...). Multi-winged aircraft must be set-up, or rigged so all the wings are "getting along" when they fly, as it were. I checked the manual and plans, and Sig did not include any mention of stabilizer or wing incidence. I measured the stab, top and bottom wing chords against the thrust line. All three are set at zero to the thrust line. This is an area that you want to measure. Some builders put in minus -1.0 to -1.5 degrees incidence on the top wing so both wings do not stall at the same time.
Was the recommended .60 size engine a 4 stroke or a two stroke?
2-stroke because:
- when this models was offered, there weren't any production .60 4-stroke engines
- the box depicts "Engines: .60"
if the motor IS over-powered for the plane? , the plane is flying faster at full throttle than design speed, as you say - therefore there is more lift and the plane would tend to climb? - do you think the additional prop wash over the wings especially the lower one is also a big factor?...
No. Prop wash does not cover that large a percentage of the wing that it would make such the difference that you are experiencing.

EJWash

[mcnamajp]

Yes there WAS something else... This Skybolt has always flown with a little down elevator so I didn't think too hard on the plane flying unusual when I flew it after some crash repairs but in the harsh light of dawn I realize this time it was really climbing out harder.
Well after my last post I undertook to increase down thrust and now have 5.7 deg by grinding the motor mount - it's easy to get too much my first install with pre-existing shims (2) was 7.4 Deg down and 4.5 right; I removed one shim and I'm at 5.7 Deg down 3.1 right. (I'll probably be taking the other shim out soon....) I was in the heat of "battle" making the change when you replied back... in the process I broke the throttle control rod and had to remove the wing and struts etc. to get inside to the radio. I had installed the pack and battery the way the previous owner did (good enough for him good enough for... :censored: ) Well after I got the wing off I found the battery pack and receiver shifted back so my CG had moved aft of where it was when I checked it before flying. I don't think his battery and receiver shifted with his friction fit method, but for me it did.... So I re-did that with a glued brace keeping it all in place. CG is back where it was, but I've got the 5.7 deg down thrust - most likely too much... Historically with 3 deg it still climbed too hard with high thrust (in my opinion). As a side note - you couldn't install the cowl with any more down thrust than this without cutting the cowl front opening on the lower edge...
I'm going to fly it tomorrow to see if it cured the old fly with down elevator condition. It would be nice to throttle up and have it accelerate straight and level but I'm expecting it to actually descend on power :censored: that will be weird... I'll let you know! Thanks for the hard thoughts and advice.
Don't know how squirrel-ly this could be...
I'll check for any advice before I fly tomorrow :eek:

[EJWash1]

Well, isn't the simple explanation always the case? The first advice should have been to check to see what you have at present as far as C.G.. Check, and check again. :D

I would take out the down thrust and go with a close to 3 degrees as you can, and still check the incidence before you fly since you advised some pitch change with power. Maybe the shifted C.G. amplified it.

EJWash

[mcnamajp]

I do believe that the CG change amplified the problem - but it did get me going to try to fix the annoying trait... This Skybolt has always needed the slight down elevator to fly at about 1/2 throttle and less down elevator as engine rpm decreased. On throttle increase it always has climbed out. Since my CG was checked with fuel tank empty even with the battery and flight pack shift, I think the CG wouldn't have been too bad.
Horizontal stab and lower wing appear to have zero incidence angle however the upper wing has about a 1.4 deg positive incidence angle - maybe those "ca-pains" are wrong after all. The measured difference is that the leading edge appears to be .2 inches higher from the thrust line than the trailing edge; since wing chord is about 8.25", this calculates to the 1.4 deg angle.
So I had about 3 deg engine down thrust all along but it climbed more than I liked under power and trimmed at half throttle with slight down elevator. Would this all be due to the 1.4 deg incidence angle of the upper wing? If so do you think I could compensate with more than the 3 deg down thrust?
I'm inclined to try to fly it with the 5.7 deg down thrust I now have to see the effect I'm expecting maybe an over compensation for the problem - what do you think? If it over-corrects then ok maybe I could split the difference at 4 to 4.25 deg? Now you have me wondering about that upper wing incidence angle...

[mcnamajp]

I just made a better measurement and I believe the upper wing has about a 2.7 deg positive incidence angle relative to thrust line... I can really only measure it at the root near the fuselage with any accuracy.

[EJWash1]

I do believe that the CG change amplified the problem
I agree.
Horizontal stab and lower wing appear to have zero incidence angle however the upper wing has about a 1.4 deg positive incidence angle - maybe those "ca-pains" are wrong after all. The measured difference is that the leading edge appears to be .2 inches higher from the thrust line than the trailing edge; since wing chord is about 8.25", this calculates to the 1.4 deg angle.
So I had about 3 deg engine down thrust all along but it climbed more than I liked under power and trimmed at half throttle with slight down elevator. Would this all be due to the 1.4 deg incidence angle of the upper wing? If so do you think I could compensate with more than the 3 deg down thrust?
The top wing positive incidence is the culprit. Think about it, trimmed for level flight. Increase in thrust equals more lift yes, but the upper wing a already "armed" for a climb being hard-set at a positive angle. Remember that I mentioned that the top and bottom wing have to "get along"? Well, the top wing is literally taking-off on the aircraft when thrust is applied.
I'm inclined to try to fly it with the 5.7 deg down thrust I now have to see the effect I'm expecting maybe an over compensation for the problem - what do you think? If it over-corrects then ok maybe I could split the difference at 4 to 4.25 deg? Now you have me wondering about that upper wing incidence angle...
If it were me, before I'd fly it again, I'd set the engine down thrust at 3 degree down, leave the stab and bottom wing at zero (where they both are now) and find a way to set the top wing at least at minus -1 to -1.5 degrees. I think you'll find that the wings will "get along" better at this angle, and you'll have a more relaxing flight.

EJWash

[EJWash1]

Checking the plans and build manual, during construction, the the stab is bonded to the top of the fuselage sides (see pic below of page 10) and is inline (zero incidence) with the thrust line.

Before you fly,
- bring down thrust to minus -3 degrees
- re-check bottom wing incidence at zero
- bring top wing incidence to minus -1 to -1.5 degrees
- secure battery/receiver
- check, and re-check C.G.

Do you own/have access to an incidence meter?

EJWash

[mcnamajp]

EJ, I don't have an incidence meter but I just checked one out on the internet (didn't know there was such a thing- I'd love to have one! - very slick and clever.- measuring angles the way I have been is very tedious and I really can't do it out on the wing away from the root. ( This could check for twists in the wings on any model as well). Now that I've convinced myself that I have nearly 3 degrees of positive incidence in the top wing at the root I'm convinced this is the problem too. I fully intend to change it.
In looking back at your earlier post the 1.0 to 1.5 negative incidence recommended for the upper wing causes it to stall second - great idea! stalling the upper wing last would add stability to a softer stall wouldn't it. My upper wing has been stalling first - given that it is mounted forward of the lower and is the larger wing - it would nose down very hard - with the larger moment involved stalling a tip would really flip the plane around too. Why would Sig recommend zero incidence on the top wing? Will you build to -1.o to 1.5. I'm anxious to try the 1.0 to 1.5 neg incidence. Gee if I was reaaly motivated I could build two sets of struts one for zero and one for -1.5 or adjustable ones!
It will take me a bit to rearrange a 4 degree change in the upper wing... I'm not sadistic but I'm really curious to try the plane with the 5.7 deg down thrust - how do you think it would fly? The radio and battery short of a crash will never move again, I put the nails in that coffin.
(mechanics of this site? - how do you refrence a quote from me the way you do in your reply?)

[EJWash1]

(mechanics of this site? - how do you refrence a quote from me the way you do in your reply?)
It is easier to follow this explanation if you open an additional browser window, sign on to RCG, and pull up your Skybolt topic. You will be switching back and forth between these two windows just for this explanation only. You do not have to open additional browser windows when making a quote on RCG. When I tell you to "click" on a button or box, do it in the second window, leaving this one to read from.

Go to my post #14 (post numbers are located in the upper right corner of the message outline box). Look to the right lower corner of the message outline box. You will see a blue box with the word "Quote" in white letters. click the "quote" box. You should see what is in the first pic.

You should see:

[] with "QUOTE=EJWash1" inside of these brackets at the beginning of the text to be quoted, and [] with "/QUOTE" at the end of the quote. Think of these brackets as quotation marks. All text between these brackets will appear in the post in the white boxes (see second pic).

Under the box that you type your text in, you'll see two buttons, one marker "Submit Reply", and "Preview Post". Preview your post before submitting your reply.

Scroll further down and you will see a button marked "Manage Attachments". Click this button and you will see what is in the third pic. Click "Choose File" and select the location and file that you want to attach to a post and select "upload".

Play around with these features. It takes a little practice.

EJWash

[EJWash1]

EJ, I don't have an incidence meter but I just checked one out on the internet (didn't know there was such a thing- I'd love to have one! - very slick and clever.- measuring angles the way I have been is very tedious and I really can't do it out on the wing away from the root. ( This could check for twists in the wings on any model as well). Now that I've convinced myself that I have nearly 3 degrees of positive incidence in the top wing at the root I'm convinced this is the problem too. I fully intend to change it.
I have a digital incidence meter. I love it. Some don't use them, but as long as the issue is addressed, no worries.

I have a Hostetler Plans 1/4 scale Skybolt kit that is drawn after the Sig plans. The plans depict -1 degree incidence in the bottom wing. I will build the Sig kit with zero on the bottom wing and -1.5 on the top. If that flies well, I may consider doing the same on the big one.
Gee if I was reaaly motivated I could build two sets of struts one for zero and one for -1.5 or adjustable ones!
The advantage to you situation is that the builder modified the kit with those cabanes. It will be quite easy for you to make a set with the proper incidence.
It will take me a bit to rearrange a 4 degree change in the upper wing... I'm not sadistic but I'm really curious to try the plane with the 5.7 deg down thrust - how do you think it would fly?
Not recommended! You'll just experience a more wild flight with thrust changes.

This is my incidence meter:

http://www.horizonhobby.com/Products/Default.aspx?ProdID=HAN192

EJWash

[mcnamajp]

EJ, I bought the Robart incidence meter and it is pretty great. I've now taken all the twists out of the wing - which there was much of. The wings are reasonably uniform now. It turned out the bottom wing was slighly negative at the root and 2 - 2 1/2 deg negative at the tips. I reworked it and it is fairly uniform to zero. The upper wing varied from 2.5 degree positive down to zero at one tip. I took the twists out of it and now I'm finishing up the fuselage struts that should give it a -1.5 degree uniform incidence - just need to complete the outboard wing struts now. I decided not to fly on your recommendation with the 5.7 down thrust - I also realized that the plane would be very hard to taxi. So I'm backing off the down thrust to 3 deg. I'll probably have it all together today. It's raining for a few days now but the next good flying day I'm hoping to fly and experience a much better flight behavior. Thanks for all your help! I'll give you an update on that flight. When are you planning to build your Skybolt?
Jim

[EJWash1]

Hey Jim,

Good news in the results of the incidence check. Since the Robart is analog (needle/scale) did you have to level the horizontal stab to use it? My AnglePro is digital and the reading can be zeroed out at any angle. I always secure the model to the bench and use a small carpenter-type level and level the stab anyway.

I won't be getting to my Skybolt until late summer/fall. Too much non-hobby stuff going on, and Momma WILL go on vacation with or without me... For now, I'm "chipping away" at a Citabria a few hours a week.

EJWash

[mcnamajp]

EJ, I did have to level the Stab to use my meter and kept checking it to make sure it didn't change as I rocked the model - moving things around. I'm done!... that was a pain!! everthing is within 1/4 of a degree of targeted values. I think I could have pretty much built a wing or two in the same amount of time... (I don't want to say how many hours) certaintly not brain surgery but tedious and with the struts everything affects everything else. So all is as it should be I hope... I have zero incidence on the lower wing at the root (it was negative before) with about 1/4 degree positive to the tips (couldn't get that out but compared to 2 1/2 warp negative 1/4 degree positive sounds pretty good lol. The top is pretty much 1.5 degree negative considering how bad the wings were warped I'm happy with that. I settled for 3 degrees down thrust in the motor and 3.5 degrees right thrust - I'll go back and mess with the side thrust if it yaws right ( I think that is pretty much where it was before).
I could not have done this without the incidence meter (surprised to see how much was wrong) and it leads me to believe that a lot of models problably have warps and such - you couldn't see it but it was there. Since this involved about a -4 deg shift in the top wing incidence angle - you can SEE the difference, the upper wing looks flatter to the top of the model.
Sooo if it climbs out nice and flys like a dream it's all worth it - right??? :rolleyes:
Jim

[EJWash1]

that was a pain!!
CA-PAIN ! ! !
everthing is within 1/4 of a degree of targeted values.
Well sir, if a QUARTER of ONE degree is within your sloppy acceptable tolerances... :D Just kidding. Sounds really good to me. I wonder what we flew around without such minute considerations In The Day...
Sooo if it climbs out nice and flys like a dream it's all worth it - right??? :rolleyes:
Jim
HA! Absolutely.

Sounds like you will be flying a totally different airplane.

As an aside, other than the big hit to the full-scale aircraft, I like the cabanes the builder came up with. They appear to facilitate easy wing attachment/removal, and in this case, made it very easy (time invested aside) to change the incidence.

Take a few high-speed taxis with it down the runway before you take it airborne so you can react quickly if it feels wrong. And when you do get it aloft, get a little altitude and see how it reacts to a slow-speed stall.

Can't wait for a flight report.

EJWash

[mcnamajp]

EJ,
Everything from takoff to landing was absolutely different! - better! It does the smoothest rolls and loops it ever did and landings and takoff are more stable and best of all when your low on the deck and you hit the throttle it just gets with it and doesn't head for the sky (slight climb). Trimmed out with ever so slight UP elevator! I told a guy at the field it was a totally different airplane to fly and then I read your post just now saying the same and it made me laugh. It was a little windy so I only flew twice can't wait for a calm day. Thanks for all the well founded advice. The 3 1/2 deg right thrust might be a bit much - it may have a slight tendency to roll right on hard throttle up - but I'm not 100 % sure...negligible. I would encourage anyone building this (or probably any bipe) to get the angles right - it changes the flight characteristics of the whole airplane.
Jim

[EJWash1]

Jim,

GREAT NEWS!!! You made my day! I'm glad it worked out.

I'm still a little puzzled on the slight climb on throttle-up. As far as the right thrust, if it's easy, go down to three, or even two and see what you get.

By the way, what prop are you running on your .91?

EJWash

[TomCrump]

I've been following this thread in the shadows. Glad that EJ was able to help you out.

A note on the Robart incidence meters. While one is good, more is better.

As you found out, moving the Robart meter is a pain in the assets. On monoplanes, I use three meters, which I own. One on the tail, two on the wings.

On bipes, I borrow a couple more meters,, so that all flying surfaces can be metered.

Using multiple meters removes the need to move a single meter around, and to keep an eye on the stab, making sure that it hasn't moved.

You can usually find used Robart meters, at a good price, at swap meets.

[EJWash1]

I use three meters, which I own. One on the tail, two on the wings..

Welcome home Tom, what'd ya bring us??? :D

The two on the wing, I take it, one at the root, the other at the tip?

EJWash

[TomCrump]

Hi EJ

It feels good to be home, but man, I had a GREAT time in Toledo ! :D :D :D

On a bipe, I check the incidence at the root, and farther out, as close to the N-strut as possible. I set the bottom wing incidence first. Then work on the top.

[mcnamajp]

Hi EJ was busy and just checked back. I'm running a 14-8 on the O.S. 91 - it is the prop size I inherited (on the plane) the local hobby shop owner/worker seemed to think it a bit aggressive... thoughts? Since I am now flying with a little up elevator I'm thinking the higher throttle adds more effect to the elevator? Certainty before when I lowered throttle I got less effect - I believe this resulted in my last crash (before all the incidence corrections) I got inverted fell off (probably a stall) - tried to loop out to correct chopped the throttle trying to improve the situation and avid the ground and found it in a hard way. I THINK if I had stayed on the throttle I might have cleared the ground or just pancaked the landing gear - it was that close.
The climb out on throttle is not bad - it does get worse as the tank gets empty as I might expect. I have flown again since last message and had some of the best landings ever with this plane. I think I may have been flying in and stalling the upper wing before - landings always seemed rough.
One mystery remains which I discovered the last time I flew - if at half throttle I switch to high rate on the elevator and loop at the full elevator up position the plane corkscrews out of the loop and comes out in a pretty steep right turn - I'm pretty sure this is more elevator than recommended. It used to do this at lower elevator settings (before the incidence changes) so I'm wondering if this might be related to wing stall I haven't tried it at higher throttle at the higher rate elevator setting - I'm flying today and probably will - I expect it to loop normally. someone at the field said he knew someone else who had a Skybolt that "snap rolled" very easy. All I know is the planes flies worlds better than it did.

[TomCrump]

I know that your question wa directed to EJ, but here are my thoughts.

On my 91 Surpass, I'm flying with a 14X6 prop. I,too, feel that a 14X8 is too aggressive.

In my experience, having a plane snap under full elevator control, tells me that there is too much throw.

[EJWash1]

mcnamajp,

Good old Tom to the rescue! I asked him about a prop for my FS-91 and 14X6 is what he passed along to me.

I don't have the manual handy, but I will check if there are control surface throws after the weekend.

EJWash

[EJWash1]

mcnamajp,

I checked the manual, and there are not control surface travel recommendations listed. I guess this kit gies back before manufacturers started listing such info.

The Great Planes is a little larger than the Sig (Sig - 51" Wingspan, GP - 57") But they do list their control surface throws here:

http://greatplanes.com/techsupport/technotes.html

Might be a good place to tune to for a start.

EJWash