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Biplane Incidence ? - 4/4/2002 8:44:16 PM   
PKAero


 

Posts: 9
Joined: 2/26/2002
From: Charlotte, NC, USA
Status: offline 		Can anyone explain the stab incidence setup for biplanes. I have flown three different versions of the Ultimate biplane over the past 10 years (Goldberg, Godfrey, & Patrick) and each have a different stab incidence and engine thrust relationship. I am not sure of the exact numbers for each, but I think the Goldberg has positive stab and engine down thrust, the Godfrey has less postive stab and zero engine and the Patrick has zero stab and engine up(?) thrust. All three seem to perform about the same. I have read somewhere that the positive stab off sets down wash created by the top wing but am not sure about this. Any thoughts?

Thanks
       Post #: 1

Biplane Incidence ? - 5/1/2002 7:45:59 AM   
Hal deBolt


 

Posts: 385
Joined: 4/12/2002
From: Sun City, FL, USA
Status: offline 		Hi PK aero,
Dupple deckers, biplanes, were my cup of tea for numerous years, so some experience.
Stabilizer setting on any aircraft is controlled so to speak by the
wing (s). Indealy one would assume you would prefer level flight
over a wide speed range, say half to full power.
Lift increases as the square of the air speed, so as you go from
half to full power there is a dramatic increase in wing lift.
At all times the stabilizer's work is to control the wing angle of
attack and in effect that of the craft,
To have no change in attitude as speed changes the stab must
create a force that is equal to the wing's force. It does that with
the tail moment arm, stab area, airfoil and INCIDENCE.
Given a certain airfoil incidence is the most efficent way to produce the needed lift. It allows the other factors to besmaller.
A biplane is no different than other aircraft except that it usually
has excessive wing area (lift) for the size of the craft. The "great"
lift must be controlled and as indicated it is best done with stab
lift, usually positive incidence.
.Thought: if the positive incidence was used to compensate for
down wash from the top wing would not the same be true for a
high wing monoplane?
From experience a most efficent biplane force arrangement
Engine thrust zero. Top wing 2 deg., positive, bottom wing zero.
stabilizer 3 deg pos. All airfoils symettrical
OK? Hope I have been of some assistance.
Good luck,

Hal deBolt [email]hdebolt1@juno.com[/email]

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hal deBolt

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Biplane Incidence ? - 5/1/2002 9:11:53 AM   
Flypaper 2



Posts: 4337
Joined: 3/29/2002
From: Kingston, ON, CANADA
Status: offline 		Hi Hal:
What a breath of fresh air. Used to fly with you at those meets down at the Syracuse club at the reservation back in the late sixtys. You and Ed Izzo [bless his soul] were flying pylon .Looking forward to your word of wisdom.

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Gord
Dreamed I was a muffler. Woke up exhausted.

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Biplane Incidence ? - 5/29/2002 7:09:59 AM   
Hal deBolt


 

Posts: 385
Joined: 4/12/2002
From: Sun City, FL, USA
Status: offline 		Hi Gord.
Late reply, seems no end to things that need attention.
I am new to this internet stuuf but already find a good, old
friends, etc, wake up and it is good to hear from them.
In western New York we had a trio of R/Cers who competed,
Ed Keck, Ed Izzo and me. We all were aggressive and the competion lead to progress, we accomplished much. Best of
all had a great time doing it,
We began with free flight, then to R/C and pattern. I stuck C/L
in between but don't recall the Eds and C/L.
When pattern became mundane we found pylon to be more
interesting and excitiing. Would guess that was it at Syracuse.
Great to know you are still modeling and hopefully enjoying it.
Be good,

Hal deBolt

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hal deBolt

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Biplane Incidence ? - 6/18/2002 6:59:03 PM   
Ollie


 

Posts: 958
Joined: 12/8/2001
From: Punta Gorda, FL
Status: offline 		Any wing, even with a symmetrical airfoil, that is producing lift has an up wash ahead and a down wash behind. The up and down wash extend several chord lengths above and below the wing. The upwash and down wash decrease as the distance above and below the wing increases. The flows around wings of a biplane interact with each other through the upwash and down wash of both wings. Because of this interaction the spacing and stagger of the wings determine the best angular relationship between them.

The strength of the upwash and downwash varies as the square of the airspeed which in turn varies as the square root of the wing loading so the best angular relationship between the wings will also vary from plane to plane with the wing loading and trimmed airspeed.

As for thrust line, its location relative to the center of drag of the whole plane determines how much thrust line offset is required. Planes with a high thrust line require upthrust and planes with a low thrust line require downthrust.

Every biplane will benefit from slightly different angular relationships unless the configurations are the same. It is a good tactic to make all the angular relationships adjustable in a prototype and determine the angular relationships by flight testing.

< Message edited by Ollie -- Jun 18 2002 2:15PM >

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Regards, Ollie

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Biplane Incidence ? - 6/19/2002 7:33:35 AM   
Hal deBolt


 

Posts: 385
Joined: 4/12/2002
From: Sun City, FL, USA
Status: offline 		Hi Ollie,
Good to have your input, we must have got your attention!
Of course there is a lot more to a biplane force arrangement than
surface incidences, wing vertical spacing is important, stagger helps in this regard.
I did a lot of experiementing and development of bipes many years ago. Reason was equipment weight and wing loading, a
reed system wieghed 1 1/2 lbs, needed slow flight so could not
overpower, only answer left was a low wing loading.
A bipe was found to fit the bill, could be compact and still have
much area.
Memory has faded as to source, could have been NACA. But info
is still clear. For max efficency wing spacing was to be 1 1/2 chords. If stagger was 50% of chord width. spacing could be
reduced to 1 chord width.
Above assumes equal size wings.
A dixtinct advantage was found with what I called "2/3 bipes"
The basic aircraft was a cabin style monoplane of sufficent size
to perform well. A lower wing 2/3 the size of the upper was added.
Airfoils were NACA 65012s
The lower wing was set at zero incidence so drag would be minimum in level flight.
When the angle of attack was changed the lower wing went to
work improving performance.
Stagger was 50% of top chord, clearance was 1 bottom chord
width.
Basically a high wing the top wing was set at a "good" angle
2 deg.
Horisontal tail was 20% of top wing area.
Tail moment arm was 40% of top span.
The last paragraph of your input was right on, the final verdict
always comes with flight testing, very much so with full scale.
Testing found the proper lift proportion to have level flight over
a wide speed range required 3 deg. positive in horizontal tail
With time this arrangement repeated well with several varieties
of bipes and proved good enough to place high in the World R/C
Chanpionship.
There also is a unusual story in this regard,
Designer Steen had put a major effort into his "Skybolt" biplane
and evaluation flights revealed much to be desired.
We had a fine mutual friend who suggested what I did worked
very well in a model, why not give it a try?
He did that and found he now had a lovely flying machine.
Sometimes we modelers can be of assistance?
OK? Do keep up the fine effort!

Hal deBolt

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hal deBolt

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Biplane Incidence ? - 6/21/2002 6:13:18 AM   
crosswind



Posts: 181
Joined: 3/7/2002
From: Lawton, OK, USA
Status: offline 		My gosh! The first RC plane I ever built was a deBolt Jenny! I got a Royal do it yourself radio kit for I think about $200 and finally got it in the air. Yellow wings and blue fuse, and I thought it was absolutely beautiful! It flew great, but I'd really forgotten about it until the deBolt name hit me in the face. Thanks for a wonderful airplane. I even managed to get it up and down with minimal damage unassisted the first time I flew. It had been test flown and trimmed earlier, and that was the last time I tried flying without an instructor until I became somewhat competent. Just wanted you to know how much that first plane meant to me, and to thank you for all you've done for the hobby over the years!

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Biplane Incidence ? - 6/22/2002 7:31:45 PM   
Martin Irvine


 

Posts: 16
Joined: 5/27/2002
From: Kingston, ON,
Status: offline 		While my experience is less than Hal's, I do like bipes and have built a number of them, the most recent being a scratch designed Nieuport 11 which flew last week for the first time.

I start with the wing and the tail at the same incidence angle, usually 2 or 3 degrees, whatever the original, (if scale) aircraft had. For something like the SE5A which had a 5 degree incidence in the mainplanes, try 5 degrees in the tail, (which had a variable incidence trimmer anyway). The result of this setup is that the engine has the same degree measurement of downthrust in flight. Both Dennis Bryant and Dave Platt with their SE5A plans do the same. With the SE, the rusult in the air is a nosedown angle, just like the original.

My understanding for differing incidences in the upper and lower wings is that to match the lift perfectly, the lower wing should have a slightly higher angle as it is working in the downwash of the upper and seeing the oncoming air at a slightly downward angle.

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Martin

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Biplane Incidence ? - 6/22/2002 7:37:57 PM   
Martin Irvine


 

Posts: 16
Joined: 5/27/2002
From: Kingston, ON,
Status: offline 		(continued)
The reason for more incidence in the top wing of some planes is to ensure that it stalls first and gives a manageble nose down stall. But if the bottom wing is working in the down wash of the upper, then with both set to the same incidence, the top will stall first anyway.

With very thick airfoils, the stab is working in a considerable down wash and needs to be set at positive incidence just to get it closer to zero effective - look at the Fokker fighters. The tail still ends up providing a downward force to balance the pitching moment of the wing.

Cheers,

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Martin

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Biplane Incidence ? - 6/22/2002 8:03:25 PM   
Martin Irvine


 

Posts: 16
Joined: 5/27/2002
From: Kingston, ON,
Status: offline 		I just realized that I should point out that the selection of airfoil, stab placement, and the general configuration of the model are all going to have an effect. The closer to a symetric airfoil, the less downwash effect on the tail and the less pitching moment of the wing.

I also remember a very good 3 part series in MAN done by Carl Risten , (from memory), on designing pattern bipes. He argued that they had some advantages over monoplane aerobatic planes and could be competative. We haven't seen a flood of bipes at pattern meets so perhaps he was reaching a bit, but he still makes a number of interesting and valid points.

Cheers,

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Martin

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Biplane Incidence ? - 6/23/2002 7:55:58 AM   
Hal deBolt


 

Posts: 385
Joined: 4/12/2002
From: Sun City, FL, USA
Status: offline 		Hi Martin.
Perhaps just a memory refresher.
In the past pattern Bipes have did well at Nats and 1st World Championship.
In near past Bipes have been prominate at the Tournement of
Champions, and one placed 2nd in 2001.
Designers could be overlooking a good thing by not considering
Bipes for pattern.
They do have some distinct advantages.
Be good,

Hal debolt

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hal deBolt

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Biplane Incidence ? - 6/23/2002 4:58:07 PM   
Martin Irvine


 

Posts: 16
Joined: 5/27/2002
From: Kingston, ON,
Status: offline 		Yes for a while there, it seemed that Ultimates were, well, ultimate! But there hasn't been much biplane activity in pattern lately.

Cheers,

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Martin

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Biplane Incidence ? - 6/24/2002 7:39:58 AM   
Hal deBolt


 

Posts: 385
Joined: 4/12/2002
From: Sun City, FL, USA
Status: offline 		Hi Martin,
Modelers, especially contestants, tend to be like sheep and
follow the leader, that is what they see as being "the thing".
Superority comes with finding what is best, not letting someone
else do it and "copy" them.
My point was aerodynamically bipes have potential advantages which can be exploited to advantage in pattern.
No one seems to be aware of that. at least enough to develope
the craft. Recently I have seen some modernized versions of what
is an acient bipe that performs outstanding, obvious potential.
The "Ultimate" is obviously a good bipe, one took 2nd place in the 2001 TOC and should have won except for pilot error.
However, the craft is far from ultimate in technical aspects, would
seem a supior design would not be hard to comprehend
Don't know your concerns or asperations but if the desire and
ability is there would hope I have added some incentive, OK?
Good luck!

Hal deBolt

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hal deBolt

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Biplane Incidence ? - 6/29/2002 12:30:23 AM   
RCJones



Posts: 434
Joined: 1/6/2002
From: Durham, NC, USA
Status: offline 		PKAero,
Do you fly at Charlotte Aeromodelers? I do and would love to talk to you about bipes. I will be flying this weekend.

Dave

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If at first you don't succeed...buy,buy again!

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Biplane Incidence ? - 7/4/2002 10:52:30 AM   
Tired Old Man


 

Posts: 11981
Joined: 2/25/2002
From: Central, CA, USA
Status: offline 		Dear Mr deBolt:

I have really enjoyed your input in this forum and one other involving biplanes. I would like to thank you for all the experience and knowledge you have shared with the modeling community over so many years.

After following the course of this forum, I would have to agree with you that the RC aerobatic arena has stagnated/fixated in the mono-wing catagory. People seem to have forgotten that nothing twists and tumbles like a "muscle biplane".

There are quite a few designs out there in the full size types that will , if properly set up and flown, outfly the Ultimate bipes, and just about all of the monoplanes. Anyone ever watch the Bulldog Pitts flown by Jim Leroy fly a live performance? You have to see it to believe it.

So far, the biplanes only limitation has been the inability to match power plant sizes with their larger, mono-wing brethren. It will be interesting to see just how well the new Pitts Model 12 performs in the aerobatic circuit.

Agreed, bipes take longer to build, and their set up is somewhat more critical that that of a mono-wing, but the end result is well worth the effort.

Another long time bipe builder/flyer,
Silversurfer

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Biplane Incidence ? - 7/5/2002 6:31:57 AM