Aeroic Gremlin, build (Aeroic donation to the 2019 ISR)

[Konrad]

I did notice that my rudder response was a lot less than what I had on the maiden. I attribute this to the huge rudder gap without the wipers installed.

I want to be clear that the rudder response issue is tied to my modification of the rudder hinging. The rudder as supplied by Aeroic does not have this issue as it uses a live kevlar hinge!

Re-living the last flight my elevator comment might be more about the elevator comp. I recall that my Gremlin had a huge downward pitch early in the deployment of crow. Looking at my comp curve I see I have a very non-linear curve. Next time out I'll try to "flatten the curve" to see it that helps keep the Gremlin in check.

 

[Doc James Hammond]

I want to be clear that the rudder response issue is tied to my modification of the rudder hinging. The rudder as supplied by Aeroic does not have this issue as it uses a live kevlar hinge!

Re-living the last flight my elevator comment might be more about the elevator comp. I recall that my Gremlin had a huge downward pitch early in the deployment of crow. Looking at my comp curve I see I have a very non-linear curve. Next time out I'll try to "flatten the curve" to see it that helps keep the Gremlin in check.


View attachment 5187

Hi Konrad - if you have 5-6mm of down elevator on crow it should sit pretty well level and can be parked.

With the high reaction 'foils it take a bit more than most people think.

Loving the fight reports!

Cheers,

Doc.

 

[Konrad]

Doc. I had more then enough down. The issue I had was with the shape of the compensation curve. I had 70% of the compensation come in with in the first 25 % of crow stick input. Yep you guessed it the Gremlin dove when I first went into crow. So I'll have to work on coming up with a new compensation map (curve).

Just so folks understand with the FrSky OpenTX you are able to not only call out the amount of elevator comp but also the shape of the curve. There is a lot that goes in to programing this properly. But in the end it really is an iterative thing. I think I'll try a point that is at 25 % stick but only has 35% of the comp followed by a smooth curve. I'll also need to check the elevator trim at the start of the "Landing" flight mode. So this is three variables in play. Gotta love gliders!

Yep, this is actually a nice feature of the airfoil. But the use of expo is needed to control it. At first there doesn't need to be as much aileron throw (drag) to get "X" roll rate at the start. Not sure how this correlates with the full aileron deflection. I still have a lot of work to do with the aileron and flap roll rates.

 

[Doc James Hammond]

Doc. I had more then enough down. The issue I had was with the shape of the compensation curve. I had 70% of the compensation come in with in the first 25 % of crow stick input. Yep you guessed it the Gremlin dove when I first went into crow. So I'll have to work on coming up with a new compensation map (curve).

Just so folks understand with the FrSky OpenTX you are able to not only call out the amount of elevator comp but also the shape of the curve. There is a lot that goes in to programing this properly. But in the end it really is an iterative thing. I think I'll try a point that is at 25 % stick but only has 35% of the comp followed by a smooth curve. I'll also need to check the elevator trim at the start of the "Landing" flight mode. So this is three variables in play. Gotta love gliders!

Yep, this is actually a nice feature of the airfoil. But the use of expo is needed to control it. At first there doesn't need to be as much aileron throw (drag) to get "X" roll rate at the start. Not sure how this correlates with the full aileron deflection. I still have a lot of work to do with the aileron and flap roll rates.

Gotcha - yes these aerofoils don't react in quite the same way as low response types so they do need a bit of fiddling with the expo. The good point seems to be that once you have it figured out, its the same fo all the surfaces so I bet you'll end up giving the ailerons the same treatment to get axial rolls.

Great stuff!

I'm just designing the replacement for the Aresti models. Loads of good improvements there!

Cheers,

Doc.

 

[Konrad]

Good point! I thought that with the size and placement of the stab there wasn't as much area upon which the deflected airflow from the flaps could work against. But add to that the fact that the fast responding elevator airfoil has a lot of power early in its deflection, I think I'll have to make the compensation curve looking a lot closer to a linear one.

It's good to have an idea as to what is going on.

All the best,
Konrad

 

[Konrad]

The Aeroic airfoil.​

This is the first Aeroic aircraft I have owned. (Yes I have 2 Redshifts but the pink slip shows these were acquired later) One of the unique features of the Aeroic ships is that they carry Doc's rear cusp'd airfoils. Now let's be honest here, few of us can really tell the difference in performance between airfoils. Well, unless you are Joe Wurts or Daryl Perkins. I know I can't tell the difference between an RG-15 from a S7012 airfoil.

But with the Gremlin we (I) see a noticeable change in the response of the surface with the cusp'd airfoils. I generally just copy a known good radio program make the adjustments for the linkage differences and I'm usually happy with the results. With the Gremlin I was in for a few surprises. The first flight while very stable "felt" flighty. I first thought I might have loose servos or sloppy linkages. (I knew I wasn't tail heavy as the Gremlin was stable (not in divergent flight). Well I learned here that the cusp'd airfoil is thought of as a high response airfoil. This means that the control surface has a lot of power for very little control deflection. Makes sense that a fast responding airfoil would feel flighty. Kind of like a gyro with the gain turned up a bit too high. So rather than train my fingers to slow down I added a lot more expo to the control surfaces than I normally use.

The second flight (after some minor repairs) felt much better in roll and pitch. (Yaw, was crap but thats another topic)! So far so good. Then came the time to check my crow setting. WOW, the Gremlin dove for the ground early in the deployment of crow. Why? In full crow I was able to get a steady level trim (Doc calls this parking). But at anything less than full crow the Gremlin want to act like a ground squirrel.

Well I traced this to the airfoils particularly the stab airfoil. Most of us know to use an elevator compensation curve when deploying crow. (see Attached) In the old days all we had was a rather linear "curve" (red). This was great but really only allowed for a proper trim setting at one position (full crow). We quickly learned that the elevator trim did NOT respond in a linear fashion when in crow. So when radios allowed for multi point curves we all quickly adopted curves that looked like the black one. That is a lot of elevator comp came in fast early in the application of crow. Later in cow the flaps just added drag and did not have near as large an effect of the pitch. Now with the fast powerful response we get with the cusp'd airfoil we don't have to compensate for the slow (weak control response) of typical airfoils. This is all the more noticeable for those of us that like to have unloaded stabs with rather aft CG locations. So because of the fast responding Aeroic airfoils I don't need to bias the elevator compensation curve to have near as early (fast) a response. That is I can make the curve more linear (green). This is really nice as it is much easier to match the response of a linear system rather than a non-linear system. ( I want my ships to be in trim at all points while deploying crow [modulating] the landing. Yes I'm lazy that way!)

I'd like to see Aeroic have a note in their documentation about these fast responding airfoils. Not just to add more expo to the controls but to take into account this property of the cusp'd airfoil when generation response curves.

All the best,
Konrad

P.S.
Yes, I notice that the total amount of comp needed appears to be less. Not sure what all the variables are but with the Gremlin I did have to remove some of the comp as compared to what I was using with some of my other 60 inch ships.

 

[Wayne]

I don't recall having a curve for my elevator compensation, but I tend to feed flap in slowly, not just kick it to full. I generally will feed it in slow and burn off the speed. I may well be compensating with the stick and not be aware of it as I am usually approaching my landing area at the same time. My final goal is to not fight the plane when the flaps are down, and a simple compensation has always worked for me.

With this said, I do occasionally flip in a lot of flap to act as a speed brake and that has never been an issue that I recall. It has been a long time since I flew a Gremlin though..

 

[Konrad]

I too don't throw in full crow. I modulate crow much like I do the throttle on a powered ship. As a result most of my flight profile is somewhere in the mid stick position. Like you my goal is to lighten the pilot load even if it means more work for the programer.

That's another good point, the compensation is speed dependent. Even if I can get the ship to park in the landing pattern. If I use these same setting and pull full crow at the bottom of a dive the ship will balloon up, maybe even loop despite what comp value I have in the curve.

 

[Wayne]

Keep playing.. I use the throttle trim as my compensation adjuster and it has worked very well for me. I adjust in flight without taking my eye off the plane.. Not sure you can adjsut a curve in this manor.. never tried it.

 

[Konrad]

Yep, I too use inflight adjuster for the "gross" end point setting. This really is 90% of the issue. But like you said I don't know how to change the shape of the curve on the fly. I get the model trimmed so I can land without scaring me. I trim the flight mode "Landing" (just before the flaps start to move) . Then I move to the 1/4 point and note which way the model pitches. I do this for the 1/2 & 3/4 point. Land and make a guess as to how much I need to change the value in the programming. Rinse and repeat. Yes, it takes me about a dozen test flight to get any of my ships anywhere near being in full trim.

NEVER TAKE ONE'S EYE OFF THE PLANE. Learn the feel of the TX before one flies, or else suffer the consequences!

Show us what you are working on..

That might make finding the glide portion a bit difficult. It is advised to keep power and lift/drag controls separate. Per the lift equation power is to overcome drag. Now with gliders we can't change the power variable but we can control the drag. So on the other side of the equation adding...

forum.alofthobbies.com

 

[Konrad]

I was at Sunset Beach 2022 and the air was perfect latter in the day on Saturday for the Gremlin. I've only flown him about 5 times. What I've learned is that the Gremlin is a high energy ship. Today I was having a lot of fun actual knife edging the Gremlin back and forth much like we would a powered plane. Now the loss of heading was actually a result of having so much wing area to the incoming air. It was not an elevator trim issue. This told me the CoG was close to right on.

Now earlier I was watching some Ahi flipping around without a care to gravity. This gave me the idea to play with the tumbling maneuvers. I was able to pirouette both in the vertical and horizontal. The rudder and side area allows for this. Unfortunately at one time I lost too much energy and allowed the Gremlin to just drop out of the air. By the time I regained flying speed I hit the front side of the cliff close to vertical.

I severely damaged the fuselage stripped the rudder servo (large rudder put a lot of load on the servo gears). But I think I can save him. And the fact that the gremlin isn't a light air ship and weight built up shouldn't be easy to notice.

I hate to loose a model with so few flights. And as I was starting to understand what kind of ship the Gremlin is. I think I need to do justice to this model and try to fix it.

 

[Hank GB Z]

Well I’m sorry to hear she crashed but I am glad to hear you’re going to try to fix her. Your threads on repairing models are really good. I think I learn more from them than the build threads.

Hank

 

[Konrad]

Failure analysis. I have far too much experience with that!

 

[Wayne]

I was flying at the sametime and saw out of the corner of my eye someone launching what looked like a Le Fish, and thought they were crazy as it was blowing hard and not at a great angle. Could not imagine a Le Fish surviving these conditions. Turned out to be the Gremlin. Sad to see the results..

 

[Konrad]

Triage has started.
Here you can see that the fuselage damage isn't all that severe. But almost all the tears are associated with force concentrators (stress riser)
Here I've pieced together all the part into alignment with thin CA. CA offers no strength but is used to help get the parts in alignment. The next step is the sand off the paint and roughen the inside to allow for some proper epoxy and glass layup repairs.

The damage to the wings was very light. I lost an alignment pin. Easy enough to replace. I also lost a wing retention block. If Aloft has the Topmodels retention pins it should be easy to replace.The servo tray is totaled again easy enough to replace. I also lost the gear set for the rudder servo. I'm going to take the opertunity to down grade from an X0-8 plus to an X0-8 as they both share the same gear box. This will save me a whopping 1.5 grams in the tail.

 

[Konrad]

I was flying at the sametime and saw out of the corner of my eye someone launching what looked like a Le Fish, and thought they were crazy as it was blowing hard and not at a great angle. Could not imagine a Le Fish surviving these conditions. Turned out to be the Gremlin. Sad to see the results..

I may be crazy. But not because I was flying the Gremlin. He was flying just great. Until I made the unforced error and lost all airspeed having too much fun!

I seem to recall you having a few Gremlins but that they were sold out from under you. YOU NEED ONE!!

 

[Wayne]

Didn't think you were crazy at all.. Only if it had been a Le Fish.

The Gremlin would have been doing some huge acro in this air.

 

[Konrad]

It is a huge acro ship for strong lift slopes. Rolls looked like a drill bit and the flat spins were something to behold. It just all ended far too soon!

 

[Doc James Hammond]

It is a huge acro ship for strong lift slopes. Rolls looked like a drill bit and the flat spins were something to behold. It just all ended far too soon!

It could be better because now I have changed the manufacturer. Now the model can built far lighter and stronger than Zhou could dream of. I also changed the fuselage design to include provision for electric setup - but I'm not sure if it's worth producing.

Half of the Gremlin's problem is its name, as I hadn't realized that in the USA it was the name of a POS car.

Maybe if I changed the name?

Any inputs?

"Slope Reaper III" ?..."Fluffy" ??.. "Fireball XL5" ???

Doc - who is of course totally biased, but still likes the Gremlin's design.

 

[Konrad]

It could be better because now I have changed the manufacturer. Now the model can built far lighter and stronger than Zhou could dream of. I also changed the fuselage design to include provision for electric setup - but I'm not sure if it's worth producing.

Half of the Gremlin's problem is its name, as I hadn't realized that in the USA it was the name of a POS car.

Maybe if I changed the name?

Any inputs?

"Slope Reaper III" ?..."Fluffy" ??.. "Fireball XL5" ???

Doc - who is of course totally biased, but still likes the Gremlin's design.

A lighter ship would help a lot.

Don't know that anybody associated this Gremlin with the AMC Gremlin of the 70's. Unless they owned a Gremlin in the 70's. The Gremlin was AMC's sub compact that aimed at the same market segment as the Ford Pinto and Chevy Vega, but was of much higher quality than the other two.

If there is anything to a name. The term Gremlin in the USA is synonymous with a persistent annoying problem. Just what we don't want in our toys. But what do I know about marketing. I tried to sell a P-51 1/4 midget pylon racer as "The D.U.M.P. (Denver Unlimited Mustang Prototype)". I think I made about 80 but only sold 1/3 of them.

I think the problem with the Gremlin was that like Wayne said: they see a Le Fish. And then pigeon hole it into that class of aircraft. I also don't think the term Freestyler help. I think a term like big air airobat would have worked much better. Freestyler conjures up no constraint, care free, action. That is not the case with the heavy Gremlin.

Maybe a name change to Buzz Saw as it does spin well and it likes to cut up the air. Now when I look at the Gremlin I see a "Pelican"

While I like my Gremlin, it took me a bit of time. I don't think there is a market for it. If I had a limited budget I'd spend my $500 on a classic 1.5 to 2 meter moldie. The Le Fish and Ahi have the flipper market all tied up, even if it is on the low air side. In the air that the Gremlin flies best in, I'd be thinking of bringing out my speed ships.

WOW, a Gremlin with cheek cowls and a spinner!