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Wings Off Runup

DEFIANTLY DO NOT! There is a video floating around on youtube of someone who attempted this and it went terribly wrong, tipped on its side and was a total loss. You have way too much invested in the plane to risk loosing it all over a few more months time.

2 cents

-david
 
I have not fired up my -12 with the wings off, but I can assure you nothing like what is shown in the video would happen. The video shows a retractable gear retracting on the ground during run up. Besides, it was a turboprop. ;)

Here is an explination of the video from a friend of the builder.........
A friend of mine constructed the aircraft and installed the Walter turbine. Apparently a breaker left open by an avionics tech the day before was forgotten by the cockpit crew. This caused the downlock to disengage and the retract sequence to start. Very expensive. The prop was destroyed, engine had to go back to Walter and the right stab was broken off. The aircraft rotated/ walked around on the prop quite a distance hence the scattering cameraman. Aircraft is all repaired now and they hope to have it flying this summer.


I think you would be fine, but you didn't hear that from me. :rolleyes:
 
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Be Real

You only have 100 HP. The airframe won't even know the wings are off. Nothing bad will happen with an engine start when the wings are off.
 
I've watched several runups sans wings, including an RV6A. None was a -12, not that it would matter.
 
I ran my RV-10 without the wings on and it was probably the most powerful engine put on an RV. No WOT.
 
Geico266 said:
Apparently a breaker left open by an avionics tech the day before was forgotten by the cockpit crew. This caused the downlock to disengage and the retract sequence to start.
Click to expand...


With an electrical system design like that it was only matter of time till disaster struck, I can't imagine a system with that kind of logic :confused:
 
Wings Off Engine Run

My dad ran up his 7A w/180 h.p. CS (w/o wings) and the only issue encountered was when going wide open throttle it pulled so hard the brakes wouldn't hold it! A chain to the pick up truck solved that issue...

Doug Lomheim
RV-9A / 13B FWF
 
The other problem that may not show up after the runup is vibration and shake effects to the tail. The wings offer a lot of stability to rotary motion which may affect the tail mounting. Watch the "wet dog shake" when you shut down. Much more of that will be transferred the length of the airplane. Starting without wings isn't a good practice, IMHO.

Bob Kelly
 
First start tie down

dlomheim said:
My dad ran up his 7A w/180 h.p. CS (w/o wings) and the only issue encountered was when going wide open throttle it pulled so hard the brakes wouldn't hold it! A chain to the pick up truck solved that issue...

Doug Lomheim
RV-9A / 13B FWF
Click to expand...

The 12 only has 100 hp but it will overrun chocks at WOT, brakes and chocks should hold it but I used a tow strap from the rear tie down to a truck bumper in addition to the chocks, at first engine start.

Tony
 
Van's very specifically recommends against it for the other (non-12) RV models. I'm not sure if that applies to the 12. If it does, why would you go against their recommendation?
 
sprucemoose said:
Van's very specifically recommends against it for the other (non-12) RV models. I'm not sure if that applies to the 12. If it does, why would you go against their recommendation?
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Wow! What a response to one little question! As to "why" - my wings cannot be fitted into the workspace I have right now and I would like to do the engine related tasks and get them out of the way.

As to Van's recommendations - I had no idea they recommended against this - where is it stated?

My thought was to tie the tail off, chock, and run the first of the low power engine runs where we warm it up and then check the valve lifters. Possibly tomorrow as we are to see a rare day where it may go above freezing.

Didn't mean to start a debate!! :)
 
Wings off runup - video

Ran up my RV8 / 180 CS sans wings without issue. *However* there could have been problems stemming from a couple areas.

Video Link:

http://www.youtube.com/watch?v=JHQfhOiyKQM

Tail shake: Mine didn't seem to have a real issue with tail shake, but I couldn't have known that at the time. Its since been brought to my attention that the wings do provide a good amount of mass damping to the fuselage and will help to reduce tail shake during startup/shutdown.

The wings also contribute a good bit of weight to the tail so the plane is considerably lighter on the tail without wings. My solution to that was to tie the tailwheel spring to the rear axle of a Chevy 1500. But that still wouldn't prevent it lifting up a couple feet with enough thrust up front.

Second: the torque impulse reacted by the landing gear looked worse on video than it felt in the cockpit. In the video, you can see both gear legs flexing a fair bit as the engine stumbled to life out of a slightly flooded state. To me, it didn't feel or look unstable or apt to tip over but the torque reaction, being entirely reacted by the gear & fuselage inertia, was somewhat more than I was accustomed to.

Y'all can draw your own conclusions. I for one didn't have any problems. But, the wings definitely do contribute additional mass stability to the airplane so if you feel like you need that, then by all means put them on. I personally have no fear of a tip-over so long as the airplane is secured to something that won't move, as was evident in the video.
 
John....The simple answer. Stick the wings in, get the pins in partially enough to hold each one in. It is so easy! Tie the tail and/or the main gear legs to your pickup or some other solid object using some good rope. Use chocks as a backup and START it up!
 
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Van's forum

At Oshkosh a few years back someone asked this exact question to Van during the Van's forum. He stated that the wings are an integral part of the fuselage adding much support and rigidity to the airframe and it should never be done.

That was not for the RV-12 though but by looking at the airframe I would not guess his answer would be any different.
 
Why do it? What's the big hurry. Take your time building and mistakes will be at a minimum. There is nothing to be gained running up an engine that is proven other than you listening to the noise it makes and satisfying a desire to see another stage completed.
 
Another issue is how soon will you start the engine again after the first run. Any long term engine storage protection will be removed by the first run. If the second run is six months down the line then that cannot be a good thing. Have patience.
 
Norm, With 9+ years and 3000+ hours in the project I can assure anybody that we're not in a hurry.

The idea is to discover problems early and correct them before taking the plane to the airport. The engine run accomplished that. Next run will be when its nearly flight-ready.
 
Bill - I think there a lot of good reasons to run-up the engine prior to moving to the airport if most of your shop is in your garage with easy access. I totally get it. I contemplated the exact thing with my -8 as its a 45 minute drive to my airport. I wanted to be sure everything was working while I had the easiest access to fix any problems. I wanted to be sure when I moved to the airport the only thing left to do was put the wings on and get inspected. It had nothing to do with patience.

In the end I chose not to do it which had nothing at all to do with the video in YouTube or all the hype about the airplane will shake apart. It was more about consideration for my neighbors and the bazillion little kids running around all the time - plus having to rig up some weird fuel lines and such.

To mitigate the need to know everything was working I spent many, many extra hours pouring over every little detail of my engine installation and checking every possible hose, connection, adel clamp, prop bolt torque, blah, blah, blah... times ten. Which is probably a good idea anyway.

It all worked out for me and when I moved to the airport all I did was put the wings on and get inspected.

These airplanes are not made of tissue paper. You don't need to pretend it is a super fragile machine. You'll put more stress, torque, vibration and load on your very first landing than you ever will during a wings off start-up. I'd tie the tail down really good though and ensure you have a safe fuel set-up and keep the kids away.

my .01

Ken
 
Not sure I understand the engine check before going to the airport. The engines are new and run tested at the factory. Making hook up corrections at the airport should there be a problem is no different whether the wings are on or not. May be harmless but I wouldn't put the twist and vibration on the fuse w/o the dampening affect of the wings unless there was no other choice. Just sayin.
Dick Seiders
 
dick seiders said:
Not sure I understand the engine check before going to the airport. The engines are new and run tested at the factory. Making hook up corrections at the airport should there be a problem is no different whether the wings are on or not. May be harmless but I wouldn't put the twist and vibration on the fuse w/o the dampening affect of the wings unless there was no other choice. Just sayin.
Dick Seiders
Click to expand...

I agree totally with Dick on this.
 
BigJohn said:
Wow! What a response to one little question!

Didn't mean to start a debate!! :)
Click to expand...

BigJohn, this topic comes up fairly often and could almost be put into the "Never Ending Debates" section.

I am curious to hear if Van's recommendation extends to the RV-12 now.
 
The normal force generated by the main gear is the only force which resists the moment generated by the engine and is independent of the wings whose forces (Weight) cancel each other (provided both have the same amount of gas and were built the same). While the moment of inertia about the longitudinal axis will be lower for the wings off case and if the fuselage were permitted to rotate freely would surely spin faster, however; Since the main gear prevents rotation and the tail is not held rigidly there cannot be any twisting of the airframe - with or without wings. How much twisting load on the tail occurs during a full slip to landing at 90MPH compared to the start-up of the engine without wings?

The wings do not provide significant "damping" in the truest sense since air isn't viscous enough without rotational velocity as in a roll in which the wings create a damping effect to the aileron input causing a steady roll rate for a given stick position (all things being equal).

Certainly the combination of main gear, mass of fuselage and wings changes the resonant frequency of this spring-mass-damper system (the most significant damping originating from compression of the tires - similar to your lord engine mounts) but vibes on even the worst installation are insignificant and certainly within the tolerance of a properly constructed RV.


Provided precautions are taken to tie the tail down and safely provide a fuel source there is no VALID (none I've read yet anyway) reason why this cannot be accomplished with zero negative effect to the airplane.
 
Ken K., that is a lucid, well thought out, and technically (sounding) supportive basis for such a practice doing no harm. I still wouldn't do it. In addition, I figure Van wouldn't say it's not a good idea if it was.
Dick Seiders
 
Hey Pierre, it looks like you shut it down with your yawn. In a way it's too bad as even a boring thread contains some good information. Just my thoughts.
Dick Seiders
 
Dick.. I nearly replied just before you today, and chose instead to do so on here:
Whilst building the RV-3 fuselage, it suddenly struck me there was a discontinuity in major longerons in the lower fuselage between the main and rear wing spars...

It made me go back to the plans and check I had not omitted something... and then realised, no I had not, the "load" path is provided by the wing structure itself.

If you do choose to run the engine without the wings bolted on, think through how the "box" rigidity of the fuselage (in twist) is compromised by no wing box, and also the straight line path from engine to tail (i.e. tying the tailwheel down does not really help since there is a structure "gap" between the wing spars). Trying to quantify these elements is nigh on impossible - the only people qualifed to answer are Vans, and we know their opinion on the matter

Andy
Click to expand...
Chose not to do so here since I know nothing about the RV-12. Maybe worth checking the design to see if similar?

Andy
 
Andy Hill makes a good point as do others in this thread.

IMHO. I cannot think of any reason why anyone should do a run up without the wings attatched. The wing spar imparts extra rigidity and strength into the whole structure. It is only impatience IMO that makes people do this. After all, any engine work that you do after it has flown, will hopefully have the wings in their correct domicile.

Running the engine without wings strikes me as behaving like a street car racer. Do it at the hangar just before the first flight and sort any bugs and gotchas at the airfield.

My 2 rappens worth.
 
you don't need a continuos load path to the tail because the main gear prevents the twist to which everyone feels will be so damaging. The important load path is from gear, including the gear tower, forward. What twisting do you feel occurs with a main gear holding the fuse from rotating? The engine mount vibration dampers, main gear, and tires all dampen the minor vibratory motion. The main gear structurally supports ALL of the tortional load as the only contact point aft of the gear is the T/W which is free to pivot rotationally about an axis parallel to the fuslage at the point where the T/W contacts the ground, so very, very little load can be imparted to the tail structure. Now if you tied down the horizontal stab at each tip very tightly with a rigid structure (something with very low elasticity) I would agree it would be a risky idea as the risidual vibratory loads not damped by the engine mount, gear, tires would be absorbed through the low rigid body system of the emp and tail cone. Deflate the main tires by 10-15PSI and I'd bet you could'nt even feel the motor turning at the tail.

The fact it has been done safely many times is proof enough.

It is not impatient to want to be effecient...

Someone please present an analytical explaination rather than "I just think its bad"

I'd seriously like to learn why it is bad if I'm wrong?
 
I didn't get a t shirt

Been there, done that, no problem. I didn't get a t shirt.:)
 
Very interesting comments. One question: why does anyone feel it's so important that first engine run be done before the wings are on? I've heard some reasonably good sounding comments on why it wouldn't hurt the fuse, but none that justify doing it in the first place. Especially in view of the fact it just might be harmful to the airplane.
Dick Seiders
 
Torque

The formula for HP and Torque is:
HP = RPM x Torque (Ft-Lb) / 5252
Inserting values for the RV-12 into the above formula:
100HP = 2150 (Prop RPM) x Torque / 5252
Solving for Torque:
Torque = 100 / 2150 * 5252
Torque = 244 Foot Pounds
If the engine were locked up and you grabbed the propeller 3 feet from the hub and pulled down with a force of 81 pounds, you would be applying a torque of 244 Foot Pounds. Doing that is unlikely to damage the airframe.
Someone please correct me if my math or reasoning is incorrect.
I agree with RV8R999 and Pierre Smith.
What we are dealing with here is fear of the unknown. But evidently others have run their engine without wings on the aircraft, and their fuselage did not twist up.
On the other hand, look at what could happen:
Ren%27s%20DSC_0122b.jpg

Joe :D
 
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Dick - I strongly considered it for logistical reasons. The airport is a 45 minute drive. My entire workshop is in the garage. I wanted to be sure everything was working (electrical, EI, sensors, pumps, hoses, idle, blah, blah) where I had the tools and easy access to fix without issue without having to plan a trip to the airport. It was not about impatience but efficiency. In the end I chose not do it because of my neighbors and not because the airplane would have been damaged. Turns out my #2 CHT was going pretty high at idle right off the bat. I spent a fair amount of time reconfiguring my forward baffles and troubleshooting this problem at the hangar. If I would have run the engine prior to transport to the hangar and putting the wings on I could have fixed the issue in a day rather than spread out over three consecutive weekends = efficiency. I feel this is a valid enough reason to do it. Wish I would have.

Ken
 
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