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Rotating engine nacelles...

Old 12-17-2003, 11:51 PM
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tiggerinmk
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Default Rotating engine nacelles...

Ok, I've skimmed the entire forum and can see that there are various ideas and designs out there for VTOL aircraft. Many of them have one thing in common. The need to rotate an engine housing / nacelle from horizontal to vertical.
This seems to me to be the main mechanical challenge. Most of the other challenges I've seen are connected with control and stability.

I'm sure there are some completed (successful?) models out there, so please show your ideas for connecting the engine housings do that they can be rotated from within the fuselage. Ideally, this would involve components that are readily available that don't require a shop ful of power tools to produce...
Old 12-23-2003, 02:18 PM
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Default RE: Rotating engine nacelles...

ok i'm almost 16, using tools borrowed from the shed, using a desk which should be used for school work and building in my tiny little bedroom...if i can do it successfully then you have nothing to worry about! lol

on mine (copy of vertigo) i've bolted my engine to a flat piece of 1/4 ply wood 6inches x 3 inches. Servos and fuel tank etc is put on behind the engine. I then attached a spruce spar to the underside and rounded off both end of the spar. I'm going to put this in something which will let the nacelle roll from vertical to horizontal and vice versa so this is my way of doing it, hope it helps.

Also got a retract servo connected to a bolt put through the spar (acts as a pivot) and this turns the nacelle from horiztonal to vertical
Old 12-23-2003, 04:38 PM
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tiggerinmk
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Default RE: Rotating engine nacelles...

OK, I had some further thoughts on this.......

Since posting, I've seen a couple of very complex Osprey projects using helicopter heads and connected transmissions. However, I'd like to take a far more simple approach and treat the Osprey type aircraft like an aeroplane rather than a helicopter. After all, that seems to be the way that Realflight treats it, as all the flight surfaces have conventional controls, and the engines appear to be turbo props which on a full scale would be constant speed and variable pitch but on a model can be dealt with using fixed pitch with a throttle.

So, take one high wing trainer kit and build it using some dihedral and with a wingspan of around 3/4 original. Make up two engine nacelles. I have a twinstar NIB so constucting nacelles should be no problem. The idea is very similar to taking a single engined plane and creating a twin, except that the nacelles are on the very end of the wing and can be rotated. Take a SIG LT-40 for example, using two 35-40 sized engines should be enough to give the aircraft plenty of vertical power....

Mounting the nacelles....
Ideally, the nacelles should be rotated around their balance point; this would reduce the stress on a servo to move the nacelle. In practice, the engine mount looks like a good place. The engine mount will have built in sleeves to mount a nose gear. So, (conveniently) using a nose gear seems like a good option. Cut down the wheel axle to the thickness of the firewall and drill a hole for the axle in the firewall. Obvoiusly, you'd need to cut the gear just before the spring, but there should be enough length for it to extend a fair way into the wing. You can use the plastic gear mounts to secure the gear in the wing to a suitable hard point. The steering arm can be used for connection to the servo. It would probably be a good idea to build an access door in the wing so that the linkages could be maintained.

Servos:
The throttle servo can be mounted behind the fuel tank in the nacelle as is usual practice. You need to make sure that the servo wire has enough slack to allow rotation of the nacelle. I would prefer a high torque servo for the nacelle operation as it will allow proportional use whereas the retract servo won't.

Electronics:
As I stated above, I'm treating this like a twin so nothing complex is required. However, there is a circuit available that will allow almost perfect syncronisation of the engine RPM's. This would be advisable.


Balancing:
As per a 'normal' aeroplane. CG slightly forward if possible as the fuel tanks are aft of the CG. Move all the fuse housed electronics into the fuel tank are to aid balancing.

Testing:
Set up the nacelles with a couple of degrees downthrust in the forward position. Test fly the plane as a conventional twin. If it flies, then you can experiment with rotating the nacelles.....
Old 12-23-2003, 04:50 PM
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tiggerinmk
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Default RE: Rotating engine nacelles...

ORIGINAL: vtol_guy
on mine (copy of vertigo) i've bolted my engine to a flat piece of 1/4 ply wood 6inches x 3 inches. Servos and fuel tank etc is put on behind the engine. I then attached a spruce spar to the underside and rounded off both end of the spar. I'm going to put this in something which will let the nacelle roll from vertical to horizontal and vice versa so this is my way of doing it, hope it helps.

Also got a retract servo connected to a bolt put through the spar (acts as a pivot) and this turns the nacelle from horiztonal to vertical
I just had a re-read of this. My main worry with this is ease of rotation of a wooden spar. It doesn't seem to create a good bearing surface. My thoughts on the nose gear rotating in plastic sleeves should hopefully be arelatively low friction solution. The main question is whether this method is strong enough for a .40 sized engine...
Old 12-23-2003, 05:41 PM
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Default RE: Rotating engine nacelles...

yeh ive decided to cover the wood rotation part in some metal sleeving epoxied on and also some metal sleeving into where it will pivot along
Old 12-23-2003, 08:25 PM
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William Robison
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Default RE: Rotating engine nacelles...

Gentlemen:

My opinions have been requested. So, for what they are worth, I'll share some with you here.

I am going to ignore normal forward flight, all the following discussion relates to the VTOL and hover only.

Most obviously, for an airplane of any sort to be supported by the engine thrust, the thrust has to be greater than the weight of the airplane. With modern engines this part is trivial, and it is the only part that is trivial.

The very first consideration is having the center of thrust and the center of gravity in the same vertical line. Not near, but the same line. If they do not coincide the airplane will not take off, but rather will roll to the heavy side as it tries to lift off. Consider a conventional airplane, lifting it with one finger under the fuselage. If your fingertip is anywhere except directly under the CG the plane will roll off your finger.

A single engine vectored thrust model has been flown, please review the "Vertigo" threads here on RCU. First flight of this plane was quite a few years ago. While a difficult plane to build successfully, and also probably hard to fly, it has been done. If you build one, I would strongly suggest you make no modifications until your second one, use the first to learn how it has been done. The Vertigo uses vanes in the prop blast for roll, yaw. and pitch control in VTO and hover modes.

When we go to multiple engines rotors, things get nastier.

I've seen some posts where the use of the throttles for roll control is proposed. Sorry, you wont find the throttle response either fast enough, or precise enough, to do it. It will have to be done through collective pitch control, either independent channels for each or one master and a second channel for trim.

Then we come to pitch control. Remember the center of thrust and the center of gravity? With our "Osprey"type plane we dont have much way to put effective vanes in the prop blast, the ailerons (if the wing tilts with the nacelle) would do some of it, but since we already have collective pitch control it is a minor matter to add cyclic control also. It would not be necessary to have roll cyclic, we already have that with the variation in the collective from side to side.

So let's review to this point. Just in the nacelles we have (remember to double this for two nacelles) one throttle servo, one collective servo, and one cyclic servo. Plus the engine, the fuel tank, and the rotor head with swashplate and linkages. And we've still not gotten to the tilt mechanism, tilt servos, the servos for normal flight controls, nothing beyond the nacelles.

Let's have some response on this, as far as we've gotten, and go into tilt mechanism in another post.

And in the meantime you can also think about the effect of an engine out on a plane of this sort.

Bill.
Old 12-24-2003, 12:53 AM
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Default RE: Rotating engine nacelles...

Bill,

Thanks for your input. Although very interesting, in terms of VTOL and hover, you are going down a very complex path that has been trodden before with mixed results. [link=http://www.geocities.com/v22chap/WelcometoR-CVTOLHomePage.html]RC VTOL Osprey Projects[/link]
I can see the point of going the 'helicopter' route for complete control of the hover, but aside from being a very costly and complex solution I feel that it is cheating in that it is significantly different from the full size application. A gallery of pictures can be found at the [link=http://www.boeing.com/rotorcraft/military/v22/flash.html]Boeing Site[/link] and at the [link=http://pma275.navair.navy.mil/]Navair site[/link] . I have also included a couple of sample pictures below....

From my (untrained) eye, it looks to me that the nacelles contain turboprop units with conventional variable pitch props and not helicopter style rotor heads.

Keeping to the VTOL aspect for the moment, my approach would be to reject the helicopter idea as too complex and cost prohibitive and go with the KISS principle of treating the aircraft like a twin aeroplane that just happens to have rotating nacelles. Although this can be taken with a pinch of salt, the G2 model seems to use this angle in that the only control for the engines is the throttle and the nacelle rotation.

This takes us back to the idea of having a pair of engines with conventional fixed pitch props (probably low pitch and large diameter) kept in synchcronisation with an RPM sensor. As for the CG of the aircraft, this would be on the wing spar as usual which would also be the pivot point of the nacelles as they would be attached to the webbing between the top and bottom spars using possibly the method I detailed above. Of course, care would also have to be taken to ensure that the plane is leterally balanced. As for stability in hover, this cannot be absolute as we are not designing a helicopter. Instead we have to rely on the available effectiveness of the control surfaces perhaps aided by a gyro or co-pilot.
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Old 12-24-2003, 05:46 PM
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vtol_guy
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Default RE: Rotating engine nacelles...

single engined vtol's are much easier to do hence why i've switched to building my vertigo varient. I'm very well on with it so should have a flight soon! :-)

Mine is using all plane components too...no expensive heli rubbish on my bird (except gyros) lol
Old 12-27-2003, 07:11 PM
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Default RE: Rotating engine nacelles...

tiggerinva, It sounds like you're going down the same sort of track as me.
My idea for the rotation of naccels uses 1 complete shaft inside 6 bearings. The shaft will have an arm welded on at the center, with a ball-linked rod to 2 BIG servos. I think it will be best to have plenty of power to control these naccels, I will use large 1/4 scale / sailing servos for this task.
The tips of the shaft will have arms welded on, providing structure and surface area to fix the naccels(carbon fibre moulded) onto.
My shaft will be the CG point, and also form the main spar in the wing.

It sounds like the contest of treating a vtol as a heli/plane will run and run, as will twin v single, but I think that the twin plane approach is by far the simplest and most appealing.
Has anyone actually had full forwards transition using the heli-twin approach? Dont think so! - chapman crashed his ospray trying it.

As for hover-roll control, as I've said before, I'm using a fresh approach by ducting air through the wing from a d.fan, varing flow with a sliding 'trap-door' mechanism, and diverting flow downwards at the outlet. The same system will be used in the tail for yaw&pitch. All three controls will have gyro input when in the hover state.

Another roll controll solution that I dreamed up:-
Using a build up wing, make a double trap-door on the top+bottom of the wing, directly under the prop blast. By altering the amount af air allowed through the middle of the wing, it will change the reletive vacum under the wing, therefore control roll.

Personaly, I'm not keen on the idea of puting a tank and servo inside the naccel. So I hope to feed the engines from the fuz, and have a standard throtle cable fed into each naccel.
I'll use 2 of those big black tanks in the fuz, and give it plenty of pressure from the 2 RCVs and the d.fan engine.

tigger, I very glad your talking about the rpm sync gizmo, where can I get one from? I need it on the shopping list.

sam, I've never known anyone build as fast as you, in a rush?
Old 12-27-2003, 07:21 PM
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vtol_guy
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Default RE: Rotating engine nacelles...

me in a rush? lol, definatly!

i've got 2 weeks total off time of school, my evil mother says i'm only allowed to building when there is no school because "i have to concentrate in exams and do my best so i can get a good job and earn a living" lol


mothers ey who needs 'em!
Old 12-28-2003, 12:11 AM
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tiggerinmk
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Default RE: Rotating engine nacelles...

Here's the link to the engine synch device: http://www.emsjomar.com/ Select electronic accessories from the menu on the left and scroll down.
I had a quick look around in the twins forum, this seems to be the only one referenced.....
Old 12-28-2003, 12:26 AM
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Default RE: Rotating engine nacelles...

Tony:

The EMS synchro device is the only one currently on the market. You will need metal discs on the engine to mount the magnets for the RPM sensors, and ball joint throttle linkages for absolutely no slop.

A different note - the V-22 Osprey does have cyclic as well as collective pitch control on the rotors/props.

Bill.
Old 12-28-2003, 11:42 AM
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Default RE: Rotating engine nacelles...

Thanks tigger, I've been googleing for weeks for that!
Old 01-02-2004, 05:57 PM
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Default RE: Rotating engine nacelles...

Yes, the osprey does have full cyclic control. I havent used pnuematic retracts yet but i was thinking they could control the nacelles. Not sure of strength and weight. This seems like an easy project it just is expensive. Think simple, this isnt that complex. It is a chinook on an airplane that turns sideways, done. You will need a multiplexs mixing to accomplish the rotation of nacelles since you need to change from heli to airplane modes and not have them both at the same time. I'm thinking about buying two Quickie 18 helis(the smallest nitro heli with collective?) and modifying a spinner for the collective covers on the nacelles. I'll make a chinook first and then stick it on an airplane and rotate it.
Old 01-03-2004, 03:00 PM
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vtol_guy
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Default RE: Rotating engine nacelles...

cherikeered, you really don't need all the heli stuff on these VTOL's. Don't get me wrong it allows for much more firmer control over the model in both flight modes but it can be done much cheaply by just using props instead of rotors with collective and all that stuff. Props can work just as well as the rotors, i've seen it done before
Old 01-03-2004, 05:49 PM
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Default RE: Rotating engine nacelles...

You need cyclic if you are making an osprey, not other vtols. Although the other vtols are horrible.(except for harrier)
Old 01-03-2004, 06:55 PM
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Default RE: Rotating engine nacelles...

True, however you could mount the engines on seperate shafts and control pitch and yaw that way then roll by varying the throttle control of each engine. However if its a scale job you're wanting then heli rotors are best as they are more near the size of the rotors on the v-22! lol

IMHO here but i think that v-22 isn't really one of the best VTOLS's, in fact i think its near the bottom of the pile for me. Other designs such as the dynavert and varients made by the Luffwaffe are technologically much better, the whole idea of a tilting wing was much easier to manufacture and allowed the whole plane to be built much lighter and cheaper, also surprisingly responsive too. The tilt wings transition time was virtually instantanious, it was about the same transisition time as the harrier (if not faster). The v-22 takes nearly a minute (i think?) to transition and overall it a lot more expensive. Best VTOL ever built was the canadian dynavert but thats just my opinion i suppose when it comes to looks the v-22 does rank better than the dynavert but don't forget the bell 109, wow! lol
Old 01-04-2004, 03:11 PM
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Default RE: Rotating engine nacelles...

Be careful, when you vary throttle you will also yaw from torque.
Old 01-04-2004, 06:15 PM
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vtol_guy
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Default RE: Rotating engine nacelles...

yeh i've got that fixed out on my vtol, i'm having a gyro linked to the yaw hover vanes with gain set to maximum
Old 01-12-2004, 06:03 PM
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vtol_maverick
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Default RE: Rotating engine nacelles...

Sam,
I was reading about the jet guys using gyros for unstable planes at slower speeds, but they have to turn the gain down when flying normaly, or the controls go NUTS.
I think vtols may also need to alter gain for transition to normal forwards flight.
Some gyros use an aux channel for switching gain.
What gyros will you use for yours?
Old 01-12-2004, 06:21 PM
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vtol_guy
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Default RE: Rotating engine nacelles...

i'm using GWS PG-03 on mine, one has a switch on it so i can turn it off mid flight, this'll probaly be the pitch gyro to begin with, if need be i'll get another couple of switch's for the yaw and roll gyros. They'll be turned on and off by ch 5 undercarraige switch

got it hovering this evening but had to hold onto her (no gyros hooked up yet)
Old 01-13-2004, 07:32 AM
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vtol_maverick
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Default RE: Rotating engine nacelles...

cool
Is the PG-03 the £55 one?
My local model shop sells these 2part packs of a gyro and mini servo for about £20, have you seen these before?
Old 01-13-2004, 01:44 PM
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vtol_guy
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Default RE: Rotating engine nacelles...

not seen those 2 part gyro packs you're talking about

PG-03 are £35 last time i checked, best to get them off e-bay though, got one for £15 including the switch which costs £10 as well.

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