Besides the L-39s the 731 has also been flown in at least 7 other military trainers, including by Boeing, Textron and CASA (180+ built, in use since 1980). No doubt there are differences in oil systems etc. but the core engine can certainly handle the Gs.

In fairness- I have only logged about 1.5hrs in the jet so far. but my impression after meeting the group of people who own and fly them is that they aren't pulling 5g's, and 0g or negative is transient at most. that takes a level of dedication and work that most weekend warriors aren't committed to (ie, g currency).

I pull between 4-5G regularly. Now SIX takes some airspeed and effort to get the airplane to do. As for 0 I love inverted flight, just under 20 seconds (fuel limit)

Mat

I think the biggest risk is low proficiency in the jet. You have to fly it with energy management always in mind. In my opinion, all VFR patterns should be overheads with a tight base to final. IFR, tight vectors to final. The speeds are fairly slow and easily manageable. However, the throttle response of the AI-25 requires thoughtful inputs and outputs and liberal use of the boards. It is where many people struggle with. Formation work is actually really beneficial for teaching the penalty of pulling power vs fanning the boards.

Buffets are very noticeable and stall response is very tame - the only gotcha is really the throttle response vs sink rate. It is definitely not a fighter and it isn't a business jet. It doesn't really behave/feel like either. It still has a lot of trainer-isms to it that will keep the variety of lower experienced people safe. Every flight that isn't completely IFR should pull at least 4Gs.

The actual jet itself is very reliable and it is simple to maintain. Personally, I would trust that motor more than any certified piston engine out there. I've never flown the 731, but I imagine the reliability would be even better. Curious if the throttle response is that much better.

It has a lot of things going for it, like the ability to do battery starts and not having hydraulic flight controls. It's very hard to over-speed. The trailing link gear make every landing silky smooth. BFM in the jet is a bit like playing 1v1 basketball with two 300lb, out of shape guys. But, I will say that it handles very well and predictable under heavy buffet - as long as you have some air under you. The first notch of flaps definitely helps with slow-speed BFM.

It would be frustrating to just use it for cross countries. It does not carry a lot of gas and getting extended vectors or an early descent can get pricey, fast.

Taxiing the jet (and I feel like each L-39 is different) can be a humbling experience. Best to avoid tight parking spots. The canopy is also a weak link, need to brief passengers to use extreme care with opening procedures.

I let my friend in the back seat taxi it yesterday, and it was fun watching him learn it. Not a simple to use system for someone expecting toe breaks but honestly like riding a bike.

It's not THAT bad for cross countries, ideally just ones that don't need a fuel stop. I have 80 Gal drop tanks I can slap on the jet in all of 5 minutes per side. Takes longer to fuel them then to hang them on the jet.

I will second the vectors issue, we did a long cross country in it and found our selfs right at our reserves when we touched down.

That's a great point. Cross countries can be fun - especially formation cross countries!

Fewer and fewer airports have high penetration approaches (and less that don't require TACANs), but those can be helpful in saving some fuel when IMC.

This is great to know, thanks. I still have plenty of time left on my AI-25, but the 731 looks like a great upgrade. I just wish they could get the 731-4 to work in there (the upgrades are all or almost all -3, which has about 1000 lbs less thrust than the -4). Apparently it's an airflow problem that would require modifying the air intakes.

I heard from one of my Navy buddies, who races L39s at Reno, that this problem was solved by the guys in south Florida. trying to get more info....

I heard from one of my Navy buddies, who races L39s at Reno, that this problem was solved by the guys in south Florida. trying to get more info....

Can you get parts for the AI-25? My partner has one at Code One and is doing the 731 upgrade. It’s not a cheap toy with full garmins.. Think it’s going be over 700k. Even though we have two perfectly good Westwind I motors he is buying a Westwind Ii motor.

What would you recommend for a high altitude operator? The practice area north of me only has 10,000' total between the ground and Class A.

AI-25 seems to have a lot of parts availability. around 10k engines built. The Ukrainian company Motorsich is still overhauling them.

Nathan Jones at Code1 has purchased a bunch of parts, (and probably cores). He is one of the "go to" guys for all things L-39. I visited his shop last month and was impressed by his company's technical knowledge, and support of the AC and engine. he probably has 15 airplanes in his shop while I was there.

Jim,

Given you only have 10,000 feet to play with - I would stay as high in that space as you can. It simply gives you more options. And then stick to your numbers. I think that’s where people get in trouble - they renegotiate their limits while flying or tolerate deviations and then make those the new norm.

For us it’s easy. We’re at sea level. Also, by using a 10K hard deck, we never have to worry about the air speed limit.

I’m not an expert, but I would think your hard deck (AGL) would depend on prior experience. Do you have time doing acro? In heavy aircraft? In heavy and slick aircraft? Close to the ground? How much time in type? How much acro in type? How much with a qualified instructor and not just your buddy Billy who flies a Pitts?

Once again, I’m not an expert and it’s very easy for me to pick super conservative parameters. So, I recommend you talk with an expert or two and get their opinions. They’ll be much wiser than I.

I’ll be at Osh and happy to talk with anyone interested and show them around the plane and introduce you to necessary people.

Zeke

Zeke,

Thanks for the advice. I would answer "nope" to all of your questions but one - I have a very good instructor available. Larry at Jet Warbirds is right here and I'll be using him as much as needed if I ever pull the trigger.

Jim

Zeke,

Thanks for the advice. I would answer "nope" to all of your questions but one - I have a very good instructor available. Larry at Jet Warbirds is right here and I'll be using him as much as needed if I ever pull the trigger.

Jim