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jpspencer(at)cableone.net
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 Posted: Wed Jan 16, 2008 8:38 pm Post subject: Flight Report and question-701 |
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I can't give you a for sure answer to what your problem is but I can confidently say this:
The takeoff behavior you describe is not normal.
I don't know what the problem is but the 40# behind the baggage area is highly suspect-that much weight is huge especially to the rear. Have you calculated your t/o cg? Even tho you are "in limits" if it's toward the aft limit it will try to pitch up.
Don't go moving the stabilizer around. If you determine that it's a trim problem bend the trailing edge of the elevator. It's a full span trim tab.If you have to bend it much you will probably have to drill the rivets out first.
The elevator cable binding with right aileron is because of the offcenter control horn arrangement and while not usually normal in other planes is normal in the 701. I run my down cable loose because of this-but not too loose. (I didn't install the bungee). When it binds it causes a bunch of stress on the control system.
Good Luck
Joe
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daveaustin2(at)primus.ca
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| Posted: Thu Jan 17, 2008 6:18 am Post subject: Flight Report and question-701 |
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With all respect to Joe, I would not agree with his suggestion to bend the trailing edge of the elevator.
The Zenair/Zenith recommendation back in 1994 was to adjust the rear elevator mounts so that at cruise speed and power the trim tab is in the neutral position. This gives minimum drag. Any bending, or away-from-neutral position of the trim tab causes drag.
I adjusted my elevator mounts 14 years ago based on that advice.
Cruising at 120 mph IAS with 80 hp.
Dave Austin 601HDS - 912
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jpspencer(at)cableone.net
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| Posted: Thu Jan 17, 2008 7:23 am Post subject: Flight Report and Question-701 |
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Dave,
I understand your thinking about the drag of the trim tab and it may very well be correct. Maybe some of the aerodynamics experts could shed some light on that. However, I believe that for a given load condition there will be a certain amount of lift(either up or down) required of the tail and whether that lift is produced by elevator position/trim tab or by adjusting the angle of incidence of the stabilizer(elevator hinges?) is maybe immaterial for our purposes with the 701...the induced drag is the same due to the lift requirement being the same in each case. I stand to be corrected here. There may be a minute difference in parasite drag but at the speeds we are flying that hardly matters unless this is all about theory and not practical application, in which case I yield the floor to more qualified/educated folks.
The suggestion to bend the trailing edge did not originate with me. It came from ZAC, both in a phone conversation and in Zenair Newsletter #110 dated Jan/Feb 1999. I was referred to this newsletter(about a year ago) by Nick Heintz for trim adjustment. He also said DO NOT move the stabilizer(elevator hinges?) unless ALL else fails. The article in question is written by Mr. Heintz and says to bend the trailing edge of the elevator. That is what I did and it works fine and is a helluva lot easier than moving stabilizers and such around. I have no idea is this is true for your 601 or not. We are talking about the 701 here.
Don't worry about the all due respect thing...I haven't gotten any in years.
Joe
Dragging around at 96 mph TAS in a 701
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jpspencer(at)cableone.net
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| Posted: Thu Jan 17, 2008 7:31 am Post subject: Flight Report and Question-701 |
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Dave
Correction to the (elevator hinges?) in my last post-I should have said "elevator mounts"...a reference to your suggestion that it was preferable to move the elevator mounts rather than bend the TE of the elevator. BTW did you intend to say stabilizer mounts?
Joe
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nyterminat(at)aol.com
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| Posted: Thu Jan 17, 2008 8:40 am Post subject: Flight Report and Question-701 |
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Dave,
Joe is right, On the 701 the trailing edge of the elevator had a factory bend in it to push the nose down. This was done because the original design was for Rotax 582's or light engines as such. Most people put in heavier engines so that the bend is no longer required. When I first started flying with my 701 the trim tab had to counteract this factory bend. Roger told me about straightening the trailing edge and now my trim tab is neutral in cruise flight. I don't think this same thing applies to the 601. The straightingen of the trailing edge is easy to do with a slot in the butt edge of a 2x4. No problem even with paint.
Bob Spudis
| Quote: | The suggestion to bend the trailing edge did not originate with me. It came from ZAC, both in a phone conversation and in Zenair Newsletter #110 dated Jan/Feb 1999. I was referred to this newsletter(about a year ago) by Nick Heintz for trim adjustment. He also said DO NOT move the stabilizer(elevator hinges?) unless ALL else fails. The article in question is written by Mr. Heintz and says to bend the trailing edge of the elevator. That is what I did and it works fine and is a helluva lot easier than moving stabilizers and such around. I have no idea is this is true for your 601 or not. We are talking about the 701 here.
Don't worry about the all due respect thing...I haven't gotten any in years.
Joe
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daveaustin2(at)primus.ca
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| Posted: Thu Jan 17, 2008 10:14 am Post subject: Flight Report and Question-701 |
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That's affirmative, Joe. Rear elevator mounts. I raised mine by around 1/8 inch if I remember correctly.
I admit to trying to squeeze every mph I can get from my kite! Wing root fairings, coolant and oil radiators inside the cowl etc.
Dave Austin 601HDS - 912, Spitfire Mk VIII
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jpspencer(at)cableone.net
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| Posted: Fri Jan 18, 2008 6:34 am Post subject: Flight Report and Question-701 |
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Les
I spent a little time playing with the wt/bal figures you provided. Interesting how it worked out. For comparision my 701 empty cg is at 173mm, well forward of your 373 mm. On my plane any addition of pilot, passenger fuel or baggage moves the cg aft simply because the added weight is behind the empty cg. On your plane, if my figures are correct, any additional weight added moves the cg forward, again simply because the added weight is forward of the empty cg. For confirmation, when loaded your cg runs about 10%MAC aft of mine. When empty your cg runs 14% aft of mine.(MAC is mean aerodynamic chord - divide cg by total chord to arrive at %MAC in your case 373 divided by 1430 is 26% mac empty cg position). As to the tail staying on the ground with 20 gal fuel-if the tanks are more near empty the tail will probably be more apt to sit on the ground again because the addition of fuel moves your cg forward. The position of your gear fore/aft enters into the "on the ground" situation also
I did all of this hurriedly and had to back in on some of your numbers so there were plenty of opportunities for a mistake. If anybody sees one please speak up...and don't rely on anything I say without confirming it-I'm getting old.
Joe
[quote][b]
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lgold(at)quantum-associat
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| Posted: Fri Jan 18, 2008 9:48 am Post subject: Flight Report and Question-701 |
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Thanks for looking at the figures Joe. I know I have to watch the CG carefully and will probably net-off the back of the baggage compartment as described in Ralph's (jetboy's) email.
Regards,
Les
[quote] From: owner-zenith-list-server(at)matronics.com [mailto:owner-zenith-list-server(at)matronics.com] On Behalf Of Joe Spencer
Sent: Friday, January 18, 2008 6:27 AM
To: Zenith-List(at)matronics.com
Subject: Flight Report and Question-701
Les
I spent a little time playing with the wt/bal figures you provided. Interesting how it worked out. For comparision my 701 empty cg is at 173mm, well forward of your 373 mm. On my plane any addition of pilot, passenger fuel or baggage moves the cg aft simply because the added weight is behind the empty cg. On your plane, if my figures are correct, any additional weight added moves the cg forward, again simply because the added weight is forward of the empty cg. For confirmation, when loaded your cg runs about 10%MAC aft of mine. When empty your cg runs 14% aft of mine.(MAC is mean aerodynamic chord - divide cg by total chord to arrive at %MAC in your case 373 divided by 1430 is 26% mac empty cg position). As to the tail staying on the ground with 20 gal fuel-if the tanks are more near empty the tail will probably be more apt to sit on the ground again because the addition of fuel moves your cg forward. The position of your gear fore/aft enters into the "on the ground" situation also
I did all of this hurriedly and had to back in on some of your numbers so there were plenty of opportunities for a mistake. If anybody sees one please speak up...and don't rely on anything I say without confirming it-I'm getting old.
Joe
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